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PfODerty of the United States Governn 













This manual has been prepared by the Bureau's direction to 
replace '^Instructions for the use of Wireless Telegraph Apparatus," 
issued by the Bureau October 17, 1903, and prepared by the late 
Lieut. J. M. Hudgins, U. S. Navy, to whose work in wireless teleg- 
raphy the Navy is so greatly indebted. 

Rear- Admiral H. N. Manney, U. S. Navy, and Lieut. Conimander 
L. A. Kaiser, U. S. Navy, were associated with Lieut. Commander 
S. S. Robison, U. S. Navy, in the preparation of this manual. 

This art has not yet reached a state where its instruments can be 
standardized without danger of becoming obsolete. It will there- 
fore be necessar}^ to revise this manual from time to time. The 
instructions herein should be carefully observed. 

All errors found in text or figures should be promptly reported to 
the Bureau. 

Wm. S. Cowles, 

Chief of Bureau. 
Bureau of Equipment, Xavy Defautmkxt, 

July If), 1906. 



This book is divided into four chapters. 

Chapter I contains a review of facts concerning electricity and 
magnetism which are directly connected with wireless telegraphy. 

In the course of this review the vocabulary is partly developed, 
methods of producing and transforming electric power briefly dis- 
cussed, and explanations given of electric and magnetic actions 
which \\all assist in making the theory and practice of wireless teleg- 
raphy easier to comprehend. 

In Chapter II the derivation of electro-magnetic units and their 
names are explained, and illustrations given of their use in dett^r- 
inining values of the constants and the power expended in wireless- 
telegraph circuits. 

Chapter III is devoted mainly to a comparison of the different 
kinds of wireless-telegraph sets now in service, in the course of which 
some instructions relative to their use are given and the various 
parts described. 

Chapter IV relates particularly to the adjustment of wireless- 
telegraph sending and receiving circuits, to which is added a 
description of the standard method of installation adopted, general 
instructions for installing and operating all sets, a short discussion 
of the interferences to which wireless telegraphy is subject, and the 
codes in use. 

Where detailed descriptions or instructions would break the con- 
tinuity of a chapter, they are given in full in numbered appendices 
and are only referred to in the text. 

These appendices are: 

A. — Spark voltages in air. 

B. — Description and method of construction of ship aerials for wireless telegraphy. 
C. — Instructions for fitting rigging on sliips having wdreless-telegraph sets. 
D. — Instructions for the care of Slaby-Arco receiving instruments. 
E. — Specification for receiving telephone for wireless-telegraph sets. 
F. — Instructions for resuscitation from apparent deaUi by electric shtx-k. 
G. — Regulations governing use of United States naval coastwise wireless-telegraph 

H. — Regulations for the government of wireless-telegraph stations. 
I. — Instructions for keeping log books at wireless-telegraph statioas. 
K. — Instructions for installing and operating storage batteries. 
L. — Deduction of fimdamental equation of wireless tolegraphy. 
M. — Report on the calculation of self-induction. 



They follow Chapter IV in order of their numbers, and are pre- 
ceded by the two notes referred to in the text. 

All figures and plates referred to in the text will be found in the 
back of the book, arranged in consecutive order. Figs. 1 to 51, 
inclusive, were drawn by H. D. Crocker, electrical draftsman. Bureau 
of Equipment. 


(Chapter I. 


Electricity 1 

Magnetism 6 

Electro-magnetism 8 

Electro-magnetic induction x 12 

Methods of producing currents by electro-magnetic induction 30 

Methods of producing currents used in wireless telegraphy 46 

Electric and magnetic fields 47 

Electric capacity 49 

Electric induction 51 

Electric condensers 53 

Discharge of condensers 57 

Ether waves 68 

Reflection of ether waves 69a 

Refraction of ether waves 69b 

Diffraction of ether waves 69c 

Production of ether whves 70 

Chapter II. 

Units 72 

Volt, ampere, ohm, watt 77 

(>>ulomb, farad, henrj' '. 80 

Self-induction 86 

Capacity 86a 

Combination of self-induction and capacity in oscillating circuits 87 

Difference betw'een D. C. and A. C, due to self-induction and capacity 89 

Fundamental equation of wireless telegraphy 90 

Time constants of condensers and inductive circuits 91 

Skin effect in high frequency alternating currents 92 

Capacity and self induction of straight waves 93 

Metliod of s-hortening an aerial by adding capacity in series 94 

Total capacity of condensers in series and in parallel 94a 

Chapter III. 

Mechanical work done in making dots and dashes of the telegraph code 95 

Coupling 101 

Duration of wave trains 102 

Dielectric strength of air 105 

Limitations on wave lengths 107 

Power that can be efficiently used with a given wave length 108 

Slaby-Arco sender Ill 

Massie sender 112 

Fcssenden sender 113 

De Forest and Shoemaker senders 114 




Telefunken sender 115 

Stone sender 116 

EflSciencies of different types of senders 117 

Material used as die Irrt rics in condensers 118 

Sending keys ; 121 

Spark gaps and spark point 3 122 

How etlier wave j a e;ic!ied f roni aerials 123 

Ways in w!:ich ether wavers may bo detached 125 

Arrangement of wire in aerials 127 

Kinds of wire used in at^riais 129 

High potentials from induced currents and protective devices 130 

Grounds and ground connc ctions 131 

Sending efficiency 133 

Receiving circuits 134 

Slaby-Arco receiving circuit.s 137 

Massie receiving circuits 138 

Telefunken receiving circuits '. 139 

Fessenden rea^iving circuits 140 

Stone receiving circuits 141 

DeForest & Shoemaker receiving circuits 142 

Sending and receiving circuits in general 143 

Detectors * 144 

Duration of effect in detectors 145 

Detectors and their connections in receiving circuits 148 

Slaby-Arco detector connections 149 

Combination switch for changing from sending to receiving and vice versa 153 

Massio detector connections 155 

Fessenden detector connections 158 

Stone detector connections 162 

De Forest detector connections 163 

Telefunken detector connections ! 164 

Shoemaker detector connections 165 

Magnetic detectors 168 

Lodge-Muirhead coherer detector 169 

Receiving telephones : 170 

Chapter IV. 

Tuning 171 

Types of inductances and capacities 173 

Donitz wave meter and its use 177 . 

Use of hot-wire ammeter 180a 

Importance of keeping open and closed standing circuits in resonance 181 

The Fleming cymometer 182 

Slaby measuring rods 185 

Calibration of closed receiving circuits 186 

Prevention of interference 187 

Static 1 88 

Regulation of sending apparatus 189 

Protection of low potential circuits from induced high potentials 191 

Codes 192 

TjTustallation and operation i 193 


Chapter L 


1. If amber is rubbed with silk a cliange in the condition of the 
amber and of the silk is produced which can be detected in various 

This change in condition is described by saying that the amber and 
the silk are electrified or charged with electricity by friction. Both of 
these terms are derived from the Greek word '*elektron/' meaning 

The silk and amber thus electrified attract each other and bodies 
in their vicinity, but the silk will repel another piece of silk similarly 
electrified and the amber will repel another piece of amber similarly 
electrified. Since amber and silk have no effect on each other when 
not electrified, the qualities of attraction and repulsion are said to 
reside in the electric charges, and the fact is expressed by the state- 
ment that like charges repel, unlike charges attract each other. The 
silk is said to be positively ^ the amber negatively^ electrified or charged. 
Positive and negative charges are indicated by plus ( -f ) and minus 
(-) signs. 

The charges are said to consist of static or frictional electricity. 

Bodies thus charged when not brought into contact with each other 
or with what are called conductors remain in an electrified condition 
for some time. 

Bringing oppositely charged bodies in contact generally removes 
all evidences of electrification. The charges are said to unite and, 
being of opposite signs, to neutralize each other, and the bodies are 
said to be discharged. 

Sparks accompanied by a sharp crackling sound are produced 
between highly electrified bodies when brought verj" near each other. 
After the spark has passed the bodies are found to be discharged. 

Charged bodies which can be discharged by sparking at greater dis- 
tances than others are said to be charged to a higher potential. 

All bodies, whatever their nature, are caf'able of being electrified. 

The presence of static charges of electricity can be shown by what 



are called electroscopes. One of the most sensitive, the gold-leaf 
electroscope, consists of two small pieces of gold leaf, which, becom- 
ing charged in the same sense (i. .e, positively or negatively), by 
touching a charged body, repel each other, and diverge, and show 
by their divergence the presence of electric charges. 

2. Certain bodies, notably metals, have the quality of transmitting 
or carrying electric charges through themselves and are called con- 
ductors. Bodies lacking in tliis quality, or possessing it to a very lim- 
ited degree, are called nonconductors j or insulators , or dielectrics ySUicord- 
ing to the purpose for which they are used. 

3. When pieces of zinc and ckrbon ai*e immersed in a conducting 
liquid (fig. 1) the combination is called a primary cell. If a wire is 
connected to the zinc and one to the carbon and the free ends of the 
two wires brought near each other, these ends are found to be elec- 
trified; the end of the wire connected to the carbon electrified like the 
silk ( + ) and the end of that connected to the zinc like the amber ( -- ) . 
The carbon is called the positive element or pole of the cell and the zinc 
the negative element or pole. A number of cells together is called a 
battery. The liquid in which the elements are immersed is called the 
iattery solution. If the free ends of the wires are brought together an 
electric current is established, of which the positive direction is said to 
be from the carbon to the zinc, through the wires; from the zinc to 
the carbon, through the liquid. (See fig. 2, and Note 1, Appendix.) 

The current is said to be caused by a difference of potential between 
the carbon and the zinc. It is supposed to be made up of small elec- 
tric charges transmitted through the wire in quick succession; the 
charges being produced by chemical or electric action between the 
carbon and the zinc in the liquid. 

The force .which causes the movement of the electric charges which 
make up the current is called the electro-motive force and is usually 
wTitten E.M.F. 

If the free ends of the wire in fig. 2 instead of being directly con- 
nected are immersed in another conducting liquid, as in fig. 3, the 
current will fiow through this liquid. The immersed ends are called 
electrodes. The one at which the current enters is called the pos^itive 
and tlie one at which it emerges the negative electrode. These are also 
called the anode and the cathode ^ respectively. The conducting liquid 
in this cell is called the electrolyte. 

4. If the anode and cathode in lig. 3 are made of lead (or i)repara- 
tions of lead) plates, and the electrolyte is a solution of sulphuric acid 
in water, the combination is called a secondary or storage cell or accu- 
mulator and a number of such cells is called a storage battery. The 
anode is called the positive plate and the cathode the negative plate. If, 
after a current has been forced through such a cell for a time, the wires 
from the prirrjaiy cells are discomiected and the positive and negative 


plates connected by a wire (fig. 4) outside of the electrolyte, a current 
will flow, the positive direction of which will be from the positive to 
the negative plate in the wire, and from the negative to the positive 
plate in t^ electrolyte. 

6. For con^penience, a bat^tery of primary or secondary (storage) 
cells is indicated as in fig. 5, the pos^itive elements by the light lines 
and ihejiegative elements by the shorter, heavy lines. Cells connected 
as in fig. 5 are said to be in series: connected as in fig. 5a, in parallel. 


6. A magnet situated at a distance from other ifl|^ets and pivoted 
so that it is free to move, will point toward the north magnetic pole 
of the earth, which in some localities coincides with the north star in 
direction. That end of the magnet which points in the direction of 
the north star is called the north-seeking pole, or simply the north 
pole of the magnet. The other end is called the south pole. 

Similar magnetic poles, like similarly charged bodies, repel each 
other. Dissimilar magnetic poles, like oppositely charged bodies, 
attract each other — i. e., two north poles or two south poles repel each 
other; a north and a south pole attract each other. The north pole 
is sometimes called the positive pole and the south pole the negative 
pole of the magnet. 

Wrought or soft iron can be magnetized but only retains its mag- 
netism while under the influence of the magnetising force ; steel or 
hard iron once magnetized retains its magnetization permanently, 
and special means to demagnetize it are required. 

All bodies can be electrified, but all bodies can not be magnetized. 

7. If a sheet of paper is held over a powerful magnet and iron 
filings sprinkled on the sheet, the filings will assume positions approxi- 
matel}^ as shown in fig. 6. Some force connected with the magnet 
must make the filings assume these positions, which are different 
from what they would be if the magnet was not under the paper, and 
from the way the filings are arranged, this force must act in the space 
surrounding the magnet. This space is called the field of magnetic 
force, or simply the jield of force, and the lines in which the filings 
tend to arrange themselves are called the lines of force. Their direc- 
tion at any point indicates the direction of the magnetic force at 
that point, and their number in any area, the strength of the field in 
that area. 

It is found that a small magnetic needle, pivoted so that it is free 
to move and brought near the large magnet, will lie parallel to the 
direction of the lines of force at any point at which it may be placed 
in the field, and that the north pole of the needle always points along 
the lines of force in the direction leading to the south pole of the 



The direction in which the north pole of tlie needle points is called 
the 'positive direction of the lines of magnetic force, and the direction 
in which the south pole points, the negative direction of the lines of 
magnetic force. ^ 

Lines of magnetic force are said to run from the ncy:th pole of the 
magnet to the south pole through the air, and back to the north 
pole through the steel (fig. 7). 


8. If the wire in fig. 1 is coiled into a spiral, as in fig. 8, with the 
positive direction^ the electric current as shown by the arrows and 
the battery connections, a field of magnetic force which can be 
explored by a small magnetic needle, or outlined by iron filings, as 
in fig. 6, will be found to exist around the spiral, and the direction 
of the lines of force will be found the same as those around the mag- 
net in fig. 7. If the current is reversed, the lines of force are reversed 
in direction. 

Such a spiral, when traversed by a current, is found to have all the 
properties of a magnet, and is called an eledro-rmignet or solenoid. 

The strength of the magnetic field around an electro-magnet rises 
and falls with the rise and fall of the current, and its polarity depends 
on the direction of the current. 

The 'positive direction of the lines of magnetic force which surroimd 
an electro-magnet is from the north to the south pole outside of the 
s;)iral, and from the south to the north pole inside of it. 

If the number of turns of the spiral is reduced to one it does not 
lose its magnetic character. The lines of force then form circles around 
the wire, their positive direction being shown in fig. 9. If the turn 
is straightened out, as in fig. 10, the lines of force still form circles 
around the wire, and the north pole of the exploring needle points in 
the positive direction of those lines. This direction is found to be 
always at right angles to the wire. 

9. It appears from the foregoing that what is called the positive 
direction of motion of electric currents, or charges, is related to what 
is called the positive direcjtion of the lines of magnetic force, in the 
manner shown l)y the arrows in figs. 8, 9, and 10, and, further, tl at 
the terms positive and negative as applied to electric and magnetic 
effects, and so largely used in connection with them, are purely con- 
ventional. (wSce Note 2, Appendix.) 

10. Returning now to the statement in paragraph 8 that the 
strength of the magnetic field around an electro-magnet rises and 
falls with the strength of the current, and its polarity (i e., the direc- 
tion of the lines of magnetic force produced) depends on the direc- 
tion of the current, it can be further stated that a magnetic field 
exists around every wire carrying an electric current (fig. 10). 


The direction of the lines of force in this field depends on the direc- 
tion of the current. These lines of force always enclose circles in 
planes at right angles to the wire. 

11. Since a current is conceived to be made up of a quick succes- 
sion of moving electric charges (par. 3), the above facts may be 
stated in another way, viz., that moving electric charges produce 
magnetic fields in which the Hues of magnetic force enclose circles 
in planes at right angles to the direction of motion of the moving 
charges. This has been proved to be true for single static charges. * 


12. Fig. 11 represents a primary battery, with the two poles of 
the battery connected by a conducting wire, broken at K. A straight 
portion (A B) of this wire is parallel, and at a distance from another 
conducting wire C D. When the break at K is closed, a current 
flows in the circuit, and a field of force is created aroimd the wire. 
Let us consider the straight portion A B in which the direction of the 
current is shown by the arrows, and the direction of the lines of force 
by the circles (shown as ellipses), at right angles to A B. Several 
of these lines of force arc shown embracing the parallel wire C D. 

If gold-leaf electroscopes (par. 1) are attached to the ends C and D 
of the wire C D, and if the current started in A B when the break 
is closed is sufficiently powerful, the gold leaves will be observed to 
diverge, momentarily, whenever the circuit is made or broken at K. 
The stronger the current in A B, and consequently the stronger the 
magnetic field produced, the more pronounced the indications of the 
electroscope will be. 

This shows that the ends C and D of the wire C D are electrified 
when the current is made or broken in A B. When the current is 
made, the end D is negatively charged like the amber and like the 
wire attached to the zinc element in fig. 1, the end C positively, like 
the silk and like the wire attached to the carbon element in fig. 1. '^> 

When the circuit is broken at K the electrification of C D is 
reversed, C becoming negatively and D positively electrified. A 
sudden increase or decrease of the current in A B produces the same 
effect as when the current is made or broken. 

It is to be noted that the electrification of C D is only momentary. 
As soon as the causes producing it are removed, the electric charges 
unite and neutralize each other through the body of the conductor. 

We know that when the current in A B is made, a magnetic field 
is created around A B w^hich extends to and beyond C D, and that 
when the current in A B is broken, the magnetic field disappears, 
and that the only thing common to A B and C D is this magnetic 

o By Professor Rowland, Johns Hopkins University. 


field, the lines of force in wliicli surround them both, and since we 
see that one kind of electrification is produced in C D when the 
lines of force are being created, and the opposite kind when they 
are being dissipated, we conclude that the movement or creation of 
these lines creates the electric charges that we observe in C D. 

13. In paragraph 11 it is stated that moving electric charges create 
magnetic lines of force. Now, wc see the truth of the converse, viz, 
that moving magnetic lines of force create electric charges. 

These two facts are of general application and are the basis of all 
electro-magnetic calculations. 

14. It is of great importance to keep clearly in mind the fact 
that electrification in C D only takes place when the current is made 
or broken or changed in A B. When there is no current in A B 
there are no magnetic lines of force, and consequently there is no 
electrification in C D. When there is a constant current in A B the 
magnetic field is constant and there is no electrification in C D. 

It is while the current in A B is rising or falling, and the lines of 
force expanding from or contracting toward A B and cutting through 
C D as they pass, that C D is affected. A movement of the lines of 
force is required to electrify C D, and this movement is produced 
by changes in the current in A B. 

If the ends C and D are joined to form a complete circuit, a 
momentar}' current will flow when changes in the magnetic field 
around C D take. place. 

We have just seen that a moving magnetic field in the vicinity of 
C D creates electric charges in C D. We would also find that mov- 
ing C D in a magnetic field has the same effect. The change of 
current in A B is said to induce the current in C D, and the action 
is called eJectro-magnelic induction. 

The preceding facts can be stated as follows: When magnetic 
lines of force cut or are cut by a conductor, electric charges (i. e., 
a tendency to current flow) are induced in the conductor, and cur- 
rents flow if the conductor forms a closed circuit, the direction of 
the induced currents depending on the direction of cutting. 

15. When the current in A B is rising, the magnetic lines of force 
are expanding, and cutting C D in the direction from left to rigbt, 
the direction of the momentary current in C D being as shown in 
fig. 11a. 

When the current in A B is falling, the magnetic lines of force are 
contracting, and cutting C T> in the direction from right to left, the 
direction of momentary current in C D being shown in fig. lib. 
These momeiitar}" currents or movements of electric charges in C D 
themselves produce momentary magnetic fields around C D, the 
direction of the lines of force of which are shown by the arrows in 
figs. 11a and lib. It will be seen that these lines of force are oppo- 

site in direction to those which created the current in C D. The 
field of force created around C D reacts upon A B, tending to create 
in A B a current in the opposite direction to that already in A B, 
i. e., to stop it. 

In other words, the change of primary current in A B induces a 
secondar>^ current in C D. The latter current in turn induces a 
tertiary current, which is in A B. Tliis influence of two currents on 
each other is called their mutual induction. 

16. The electric charges produced by friction (Par. 1), by 
chemical action (Par. 3), and by the movement of lines of mag- 
netic force are all identical in their properties, and the magnetic 
fields produced by the movement of these charges are also identical 
in their properties. It is therefore evident that a very close rela- 
tion exists between electricity and magnetism. 

17. We have seen that the field of magnetic force around a wire 
carrying a current or around a magnet can be mapped out by iron 
filings. In a similar manner the field of electric force around charged 
bodies can be showii by the use of various light powders. 

Figs. 12 and 12b show the electric field between unlike and like 
charges, respectively. Figs. 12a and 12c show the magnetic field 
between unlike and like poles, respectively. The electric field be- 
tween two charged bodies is found to resemble very closely the mag- 
netic field between magnet poles. In all figures it can be seen that 
in electric as well as magnetic fields each fine of force appears to 
repel its neighbor, and that they have their ends on points of oppo- 
site electrification or magnetization. If these lines tend to shorten in 
the direction of their length this tendency will cause the attraction 
between the bodies from which they proceed. 

18. It may be asked, — what are these fines of force which are not 
visible and which can not be physically grasped? The only reply is 
that we believe all electric and magnetic phe- omena to be the results 
of the disintegration of the atoms of matter or the rearrangement of., 
their constituent parts (see note 2, appendix), the movements of which 
produces tresses and consequent movement or strains in what is 
called the ether, an almost infinitely elastic, infinitely tenuous sub- 
stance w^hich surrounds and permeates all matter and all space. 

The earth is immersed in an illimitable ocean of ether, just as fishe^' 
are in water. 

We move about in a sea of it. 

What we call electric and magnetic fields are places where ether 
movements and ether stresses can be detected by the phenomena which 
they produce, and which are being described. 

An electric field is a state of strain in the ether; it can be removed 
betw^een any two points by connecting them w^th a conductor. The 
release of the strain starts movements of electric charges in the con- 


J victor. Movement of these charges produces another state of strain 
in the ether at right angles to the first. We call this a magnetic field. 

We have seen that movement of either field creates the other, and 
that the lines of force in the two fields when they are thus produced 
an^ in planes at right angles to each. When equiUbrium is restored 
one field or the other has disappeared, though they can coexist in a 
transitory state. 

It has been proved that Ught and heat are forms of ether motion 
also, and that all movements (electric and magnetic) in the ether are 
J -ropagated with the velocity of light. 

This velocity has been measured many times and found to be 
lsO,000 miles, or approximately 300,000,000 meters per second. It 
takes time for electric and magnetic effects to be propagated in the 
ether, time for them to be propagated along a wire. The wire guides 
or strikes out the line of maximum disturbance. 

19. Let us now return to fig. 11. Before connection at K is made, 
the field of magnetic force does not exist, but the wires are electrified 
by means of action between the zinc and carbon in the battery solu- 
tion. When the break at K is closed, a magnetic field is estabUshed ; 
when the connection at K is broken, the magnetic field disappears. 
Thi> question arises, — how is this magnetic field created ? How is it 
dissipated? The reply is: It is created by movement of electric 
ch irges in A B which disturb the ether and this disturbance is propa- 
gated through the ether at right angles to A B,with the speed of Ught, 
i. e., at the rate of 186,000 miles or 300,000,000 meters per second. 
This disturbance is of such a nature as to produce a state of strain in 
thf^ ether which may be compared to that produced in a piece of rub- 
ber by compression or tension. The strain is relaxed as soon as its 
cause (i. e., the movement of the electric charges) is removed. 

The amount of strain (i. e., the strength of the magnetic field) 
decreases as the distance from the moving charges increases. It 
sj)reads in all directions, but except with very delicate instruments 
ciin not be detected at any great distance from A B. 

The creation and dissipation of this state of unstable equilibrium 
in the ether, which must be brought about by some kind of movement 
in it, produces electrical movement in C D, or, as it is perhaps better 
*o say, produces electric charges in C D. CD stands in the way of 
and is disturbed by an advancing or receding wave of movement in 
the ether, originated at A B. CD is, like all other conductors, an 
obstacle in the path which creates an eddy, so to speak, in the ether 
wave and reacts however minutely on A B, because the movement of 
i}i(» (»lectric charges produced in C D also creates an ether movement, 
but in the opposite direction to that proceeding from A B. 

20. We have now reached a point where the electric and magnetic 
actions under discussion are directly applicable to wireless telegraphy, 


but before proceeding with this subject it is desirable to consider more 
fully the action of A B on C D, because the creation of electric cur- 
rents by moving or varying magnetic fields, and vice versa, is the basis 
of industrial electric power — of that used in wireless telegraphy as 
well as in other branches of electricity; and other facts or develop- 
ments of this fundamental fact ^411 appear which will lead to a clearer 
comprehension of it. 

21. In fig. 11 , C I) is shown parallel to A B. If C D is slowly revolved 
around its own center as an axis the eft'ect on it of making, breaking, 
or changing the current in A B will be found to decrease until C I) is 
at right angles to A B, when it will disappear altogether. The lines of 
force are circles at right angles to A B; they do not cut C D when it 
is at right angles to A B because it is parallel to them, and conse- 
quently no effect is produced. 

The induced effects in C D will be found to increase as it is brought 
nearer A B and to decrease as it is removed from A B. The field 
near A B is stronger, and more lines of force are created there or dissi- 
pated there than at a greater distance from A B — i. o., a greater 
disturbance in the ether takes place. 

22. If the two ends of C D, fig. 11, are brought close together, but 
without touching, and if the current made or broken in A B is very 
strong, a spark will pass between the ends of C I) at each make and 
break. If C D is separated from A B by an opac^ue, nonmetallic 
screen and the makes or breaks in A B are made to represent the char- 
acters of a code, messages sent in this code from A B can be received 
at C D when each is invisible from the other. By the addition of a 
battery to C D, similar to that producing current in A B, replies can be 
sent, and thus a crude wireless telegraphy produced. 

23. If A B is coiled into a spiral and C D into a similar spiral, 
fig. 13, the effect of making, breaking, or changing the current in 
A B is much greatqr than where both wires are straight; for the 
disturbance created in the ether — that is, the number of lines of force 
produced by the moving charges in A B — is equal, for equal lengths of 
the wire, and since a greater length is concentrated in the same space, 
the number of lines of force in that space, avssuming the current in the 
spiral to be the same as that in the straight wire, are correspondingly 
greater. This stronger field would produce an increased effect on a 
straight wire; but the length of C D is also concentrated. Therefore 
the effect is increased still more. 

24. We know that A B when coiled as in fig. 13 and traversed by a 
ciurent forms an electro-magnet (par. 8, fig. 8). The space inside the 
coil is called the corey and it has been assumed that the surrounding 
substance (excluding the ether, which is present both in the interior 
and on the exterior of all bodies) is air. It is found, however, that if 
the core of. the electro-magnet is iron, as in fig. 14, instead of air, 

2740—06 2 


the eflFect on C D is very much more powerful — i. o., the number of 
lines of force created with the same current is very greatly increased. 

This sliows that it is easier to create lines of force in iron than in air; 
or, to state the fact difTerently, lines of force permeate iron more 
easily than thov do air. The relative ease with which magnetic lines 
of force ^lT^} croiitoi i.i a substance is expressed in figures and called its 
magnetic pcrmeihlUfy. The permeability of air at atmospheric pres- 
sure is called unity, and on that basis the permeability of the purest 
wTought iron is 3,000. In other words, the same current will produce 
3,000 times as many lines of force in iron as in a body of air of tlie 
same length and area of cross section. 

26. If the iron of fig. 14 is extended to include C D, as in fig. 14a, the 
effects of changes in A B is increased still more, because in fig. 14 the 
lines of force are partly in iron and partly in air, while in fig. 14a they 
have an iron path throughout, and are conseciuently much greater in 
number. C D can also be placed inside of A B or outside of it, with 
or without an iron core, figs. 14b and 14c. 

26. Since the tendency to current flow in C D is produced by lines 
of magnetic force cutting C 1), and since on making or breaking cur- 
rent in A B each line of force cuts C D once, for each turn in C D, if 
the turns in C I) are decreased or increased, as in figs. 14b and 14c, the 
tendency to current fiow — i. e., the electromotive force —is raised or 
lowered. From this fact, and from the fact that the current in CD is 
opposite in direction to that in A B, the arrangements in figs. 14a, 
14b, and 14c are called transformers. Fig. 14a is called a closed-core 
transformer; fig. 14b an open-core trmuformcr or induction coil; fig 14c 
an air-core transformer. 

Transformers are called step^up or step-doitm with reference to 
whether the number of turns in the coil C D are greater or less than 
those in A B. Fig. 14b is a step-down; fig. 14c a step-up transformer. 
The coil A B is called the primary and the coil C D the secondary 
uyindingj and where A B and C I) have some turns connnon to both, as 
in fig. 14d, the arrangement is called an auto-transformer. Auto 
transformers are very generally used in wireless telegraph sending 

27. Referring again to fig. 13: When the break at K is closed, a 
current is started, which progresses upward through the coil, the mov- 
ing charges composing it, creating a magnetic field around the wire. 
The lines of force as they expand from the current in the first turn of 
the spiral, cut the second turn of A B in the same way that they cut 
C D a little later. They induce a current in the second turn opposite 
in direction to that in the first turn — i. e., tending to stop it. The 
same effect is produced in the third and succeeding turns. In other 
words, the different parts of the coil A B react on each other just as the 
coil C D reacts on A B. This reactive effect of the turns on each 


Other makes the rise in current slower than in a straight wire, and is 
greater when the core of the coil is of iron than when it Ls of air, 
because of the greater number of lines of force produced. 

28. We find that a stronger current is produced by the same bat- 
ter>' in a short wire, tlian in a long wire of the same size and materia' 
and in a thick wire, than in a thin wire of the same length, and we sa^ 
that this is due to the greater resisiiince of the long wire and of the thin 
wire a.s compared with the short or with the thick wire. To establish 
the same current in the longer or the thinner wire as in the shorter 
or thicker wire requires a larger battery — that is, greater E. M. F. 

It has been proved that electric movements progress along straight 
wires at the same speed that magnetic movements progress at right 
angles to them — i. e., with the speed of light. 

29. Now, we find that when the wire is coiled into a spiral aid a 
change iii the current is taking place, the turns react on each other and 
resist the change of the currert. This resistance does not depend on 
the size nor the material of the wire, but only on the amount and 
quickr.ess of the charufe in the current, and is therefore of a different 
character from the resistai ce referred to above. The resistance of a 
wire to changes in current established in it, is called its reactance, and 
during the change the total effect of the true resistance and the reaet- 
ai ce is called the impedance of the wire or circuit. 

In circuits having reactai:ce the production or progression of elec- 
trical effects is retarded. It takes longer to create a given current 
than in the same length of straight wire. It may be said, therefore, 
that coiling a wire increases its electrical length — i. e., increases the 
time it takes an electrical disturbance created at one end of it, to reach 
the other. 

The currents in C D are said to be produced by the induction of A B 
on C D. The retarding effect of the coils \v A B to the rise and fall of 
current in A B is said to be due to the self-induction of A B. It has 
bee:i shown that» the amount of both kir.ds of induction depends on 
the shape and arrangement of both circuits and the material (iron or 
air) in and around them. 


30. The currents under discussion have been illustrated as being pro- 
duced by batteries of primary cells, and for many purposes these are 
very valuable, but for the production of very powerful electrical effects 
advantage is taken of the fact, stated in paragraph 14, that when mag- 
netic lines of force cut or are cut by a conductor, electric currents flow 
in the conductor, if the latter forms a closed circuit. 

Let the wire C D in fig. 11 be bent until it forms a rectangle, and let 
it be placed in the magnetic field between the north and south poles of 
a powerful electro-magnet having an iron core. By bending the core 


into the shape shown in fig. lo, the north a id south poles are opposite 
each other and a greater number of of force are produced, because 
the distance they have to travel through the air is very much short- 
ened as compared with fig. 14. 

Exploration of the field in lig. 15 by means of iron filings or by 
means of a small magnetic needle will show that the lines of force 
extend directly from a point in the north pole to the opposite point in 
the south pole. In other words, that they are straight and parallel to 
each other, and they are so shown in fig. 15. The field is also fourd 
to be of uniform intensity, which indicates that the number of lines of 
force are equally distributed throughout its area. 

31. Now, if C D is moved up or down in the magnetic field, no indica- 
tion of a current can be perceived, and it appears that the statement in 
paragraph 14 (that when magnetic lines of force cut or are cut by a 
conductor electric currents flow in the conductor if the latter forms a 
closed circuit) is in error, but when .we consider that when C D is 
moved upward that (the field being of uniform intensity) as many 
li' es of force are cut by the bottom half as by the top half of C D the 
currents induced in the two halves must therefore be equal, and since 
both flow to the rear we see that they reutralize each other, and the 
result is zero. Another way to explain this is to consider that portion 
of the field inclosed by C D as containing a certain number of lines of 
force. Those coming in when C D is moved induce a current in one . 
direction, those going out induce a current in the opposite direction, 
and if as many come in as go out no effect is produced. 

32. If C D were straight, electric charges would be produced on its 
ends and would be maintained there as long as the cutting of the lines 
of force continued, but bending it into a closed circuit changes condi- 
tions to the extent that cutting of lines is going on all around the cir- 
cuit, some inducing charges in one direction, some in the other, and it 
is only when there is a preponderance of cutting in one direction that 
a current actually flows. This would occur if C D were moved from a 
point where the field is weak to where it is stronger, or vice versa, but 
the field under discussion is supposed to be uniform. 

If C D is rotated around one of its diameters as an axis (say the hori- 
zontal diameter at right angles to the lines of force) when C D is hori- 
zontal, as in fig. 16, the linos of force included will be zero, and wher 
vertical, as in fig. 15, the lines of force included will be the maximum 
number possible in that field, so that a revolution of 90° will make 
an entire change in the number of lines of force passing through the 

For instance, if the revolution is in the direction of the banc's of a 
clock — i. e., if the top of C D moves to the right (see fig. 17) — the 
upper half of C D is cutting lir es of force in the direction which induces 
movements of electric charges to the front, while the lower half is cut- 


ting lines of force in the direction which induces niovenieiits of electric 
chaises to the rear, so that an electric current is established in C D in 
the direction shown. 

If C D's rate of revolution is constant, a little consideration will 
show that when it has revolved through 90° and its plane is horizontal 
it is then moving at right angles to the lines of force, and consequently 
cutting them faster than when, its plane being vertical, it moves par- 
allel to the lines of force for an instant and is not cutting any; also 
that the increase in the rate of cutting is progressive from one posi- 
tion to the other. It will therefore be seen that the electric current 
produced is a maximum when C D is horizontal, and that it is zero for 
an instant when C D is vertical, because during that instant it is mov- 
ing parallel to the lines of force and therefore there are none being cut. 
It is also evident that the increase of the current from zero to a maxi- 
mum is progressive during the first 90° of revolution, that it then pro- 
gressively decreases until C D has revolved through 180°, and is again 
moving parallel to the lines of force when it falls to zero. 

As the revolution continues, that half of C D which during the first 
half revolution was cutting lines of force in such a manner as to induce 
a current to the front now cuts them in such a manner as to induce a 
current to the rear, its former place being taken by what was origi- 
nally the lower half, so that the direction of current in C D is reversed. 

Another maximum rate of cutting lines of force and consequent 
maximum of current is produced when C D has revolved thi-ough 270°. 
The current progressively increases from 180° to 270° and then de- 
creases until when the original conditions are restored by the comple- 
tion of one revolution the current has again fallen to zero. 

From the above and from an inspection of fig. 17 it will be seen that 
current is always flowing to the front in that half of C D which is 
going down to the right and to the rear in the half going up on the 
left, and that each half revolution the current changes in direction. 
Such a current is called an alternating current. 

33. This can be shown graphically in fig. 18, where the rate of cut- 
ting at different equidistant points in one revolution is represented by 
equidistant vertical lines proportional to the cutting rate, and conse- 
quently to the current strength. Vertical lines above the horizontal 
line representing current strength in one direction and below it cur- 
rent strength in the opposite direction. A regular curve is produced 
by joining the tops of these lines. This curve is the cui-ve of sines, 
because the rate of cutting and the strength of the induced current 
are proportional to the sine of the angle of revolution. " 

a Since the lines of force are horizontal, the number cut during the revolution of C D 
through any angle is proportional to the vertical movement of the extremity of the radius 
of C D which generates the angle. The amount of this vertical movement is the sine of the 
angle, and therefore the induced current is proportional to the sine of the angle. 


34. If C D instead of forming a closed circuit entirely in the mag" 
netic field has its ends cgnnected to two rings which revolve with it 
and touching these rings are the ends of a coiled wire (E F, fig. 19), 
the currents induced in C D also flow tlu-ough E F and make of it an 
electro-magnet whose strength varies with the strength of the cur- 
rent and whose polarity reverses with the reversal of the current. If 
a small magnetic needle were pivoted in E F, its direction would tend 
to change with the reversal of the current, and it can thus be made to 
indicate both the direction and the amouni of current flowing through 
the coil E F. Such an instniment is called a galvanometer. 

The currents in the coil E F are sui)j)lied from C D, and they are 
induced in C D b}Mts movement in a magnetic field. C D has become 
a source of electricity like the batteiy in A B. E F corresponds to the 
coil A B in fig. 13, and the rise and fall of current in E F will produce 
a rise and fall of current in another coil near it, just as the make and 
break at K in fig. 13 induces momentary curi'ents in C D. 

The currents in C D, fig. 13, were induced by \nterrupted curreiiL 
Those induced by E F in coils near it are induced by alternate current. 
Interrupted cun^ent was used almost entirely in wireless telegraphy in 
its earlier development. It is now being replaced by alternate current. 

35. It only remains now to make C I) produce the magnetic field in 
which it revolves, and we can disj)ense entirely with the primary bat- 
tery in A B. This can be done as follows: 

In fig. 20 instead of having each end of C D connected to a ring of 
conducting material, as in fig. 19, one ring is removed and the^othor 
split into two equal parts and an end of V D connected to each part, 
the ends of E F being adjusted so that as the split ring revolves with 
C D one end of p] F is always connected through the split ring with 
that half of C D in which the current is flowing to the front and the 
other end to that half in which the current is flowing to the rear. 
This arrangement makes the current in E F always flow in the same 
direction. It rises and falls with the current in C^ D, but does not 
reverse, because just as the current reverses in C D, E F changes ends, 
so to speak, by breaking connection with one half of the split ring and 
making connection with the other. Tlie current in E F is now said 
to be a pulsaf'nig instead of an alternating current, and the change can 
be graphically rej^reseiited by transferring the part of the curve belo\v 
the line in fig. 18 to a corresponding position above it, as in fig. 18a. 

36. The alternating current in C D is said to be rectified into a direct 
current in E F. The split ring ])v means of which it is rectified is 
called a commutator, and the entire apparatus (either with or without 
a commutator), a dynamo. 

37. With a single coil, C D, rotating in the magnetic field the cur- 
rent in E F can be made to flow always in the same direction, but in 
order to make it constant a large number of coils, equally spaced, 


must be used, so that one of them is passing tlu-ough the position 
(horizontal) in which maximum current is })roduce(i ])ractically all the 
time. If there were 10 such coils, each connected to its own split ring 
(fig. 21), and all connected to E F, the currents in each would overlap, 
so that the resultant current in E F might be indicated by a line join- 
ing the highest point of each (fig. 18b). In other words the current in 
E F is practically constant. 

38. The revolving coils are lield in place on a cylindrical drum or 
ring and the whole is called an armature. If this ring is made of iron 
the strength of the magnetic field is much increased, because the iron 
affords a path for the lines of force from one pole to the othtr and 
thereby lessens the distance through which they have to pass in the 
air. (See j)ar. 24.) 

39. The tendency to current flow in C D created by cutting lines of 
force is called the electro-motive force in C D (see par. 3), and is found 
to depend on the number of lines cut in a given time, so that the faster 
C D revolves, and the stronger the magnetic field, the greater the elec- 
tro-motive force and the greater the current produced in any given 
circuit. Now, if the current induced in C D, instead of all flowing 
through E F, is divided, so that part of it flows around the core of the 
electro-magnet (fig. 21), this current can take the place of that pro- 
duced by the battery in A B and the battery can be dispensed with. 

40. In paragra])h 6 it is stated that wrought or soft iron can be 
magnetized, but only retains its magnetism while under the influence 
of the magnetizing force. Steel or har^d iroiij once magnetized, retains 
its magnetization permanently and special means to demagnetize it 
are required. It is found that electro-magnets with soft-iron cores 
can be made more powerful (i. e.,will give a stronger field) than if the 
cores are of steel, and that electro-magnets with either kind of core can 
be made to give much stronger fields than any permanent magnet. 
Also, that soft-iron cores retain a very small part of their magnetism 
and polarity when the current is broken, so that, if the magnet poles 
between which C D revolves are made of the most elBcient material 
(wrought iron or mild steel containing no phosphorus), when C D 
stops they still retain their polarity in a slight degree. 

When C D starts to revolve again the weak field generates a small 
current in C D, which sends tliis current through the wire around the 
poles; this current increases the strength of the j)oles and conse- 
quently of the field which increases the current in C D and so on. 
This is called generating or building up, and continues until the limit 
of the power moving C D in the continually strengthening field is 
.reached, or until the iron core is saturated j in which condition no increase 
of current will increase the field. 

41. When alternating current is desired a dynamo, in order to be 
self-exciting, i. e., to produce its own field, must have part of its cur- 


rent rectified by means of a commutator. It is more usual, however, 
to drive a small direct-current dynamo by means of the same power 
which drives the larger one, the current from the small dynamo being 
used to create the magnetic field in the larger one. Such a machine is 
called an exciter. 

42. The fact that magnet poles of imlike polarity attract each other 
(par. 6) applies to electro-magnets, with or without iron cores, as well 
as to permanent magnets. So that two electro-magnets placed as in 
fig. 13 will attract or repel each other according to their polarity. 
Each line of forc^ apparently tends to contract in the direction of 
its length, and by so doing exerts a mechanical pull on the conduct- 
ors which it surrounds. 

The same effect is observed between a magnet and a wire carrying a 
current (which, as we know, has a magnetic field around it) and between 
two wires, each parrying a current. They actually pull or push each 
other according to the quality of their magnetism, which is deter- 
mined by the direction of the current. 

43. If, in fig. 17, C D, instead of being revolved by some outside 
agency is supplied with a current flowing through it in the direction 
shown, it will revolve in the opposite direction. This revolution is 
caused by the pull exerted by the field magnets on C D because of the 
current in C D, or, taking into account (fig. 21) the position of the mag- 
netic poles created in the armature by the current flowing in the coils, 
the movement of C D may be considered as being caused by the attrac- 
tion of the north pole of the armature by the south pole of the field 
magnet, and its repulsion by the north pole of the field magnet and 
the reverse action of the field poles on the south pole of the armature. 

The movement will be continuous, because, as the top of the arma- 
ture moves toward the south j)ole of the field magnet, the commutator 
acts to maintain the flow of current as before, and the consequent 
armature poles are always at the top and bottom and halfway 
between the field magnets. 

44. C D thus creates a current when made to revolve, and revolves 
when supplied with current. 

In the first instance we have seen that the entire machine is called 
a dynamo; in the second it is called a motor. Every dynamo will 
run as a motor if supplied with current. Every motor will act as a 
generator or dynamo if made to revolve in its own field. 

45. The pulling power of the motor can be made to drive another 
armature in another field. Such a machine is called a motor-gen- 
erator. It can be run with direct or alternating currents and made 
to generate direct or alternating currents of a higher or lower E. M. F. 
For this reason it is sometimes called a rotary ti^ansformer, as dis- 
tinguished from the stationary transformers already described. 



46. In wireless telegraphy the source of current may be: 

(a) A primary battery (par. 5). 

(h) A direct current dynamo (par. 35). 

(c) An alternating current dynamo (par. 35). 

(a) supplies current through an interrupter to the primary wind- 
ing of a step-up transformer (par. 26). 

(b) supplies current either through an interrupter to the primary 
winding of a step-up transformer or to a motor-generator, the -gen- 
erator of which supplies alternating current to the primary winding 
of a step-up transformer, or (6) supplies current to a storage battery 
(par. 4), which furnishes interrupted current direct to the trans- 
former or direct current to a motor-generator which furnishes alter- 
nating current to the transformer. 

(c) supplies alternating current to the primary winding of a step- 
up transformer. 

Alternating current is preferred as being more efficient and uni- 
form in action. 

Step-tip transformers supplied with alternating or interrupted cur- 
rent are part of all wireless telegraph sending apparatus. 


47. Electricity produced by friction (par. 1) is sometimes called 
fri^tional electricity; by primarv' batteries, voltaic electricity; by elec- 
tro-magnetic induction, dynamic electricity. But however produced 
and transformed, all kinds of electricity are identical, and the same 
is true of all kinds of magnetism. Wherever there is an electric 
charge, stationary or moving, emanating from the charge are elec- 
tric Knes of force which end at other electric charges. Wherever 
there are moving electric charges (currents) there are magnetic lines 
of force also, and these magnetic lines of force are always at right 
angles to the direction of the motion of the charges and to the elec- 
tric lines of force proceeding from them. 

And, finally, motion, or state of strain in the ether, which these 
Imes of force represent, travels with the speed of light, and the 
fields of force, while more pronounced and therefore more easily 
detected near the moving charges, are really all pervasive. They 
have no limits. 

48. Imagine a disturbance — say an expansion of a gas — to take 
place in the center of an immense rubber ball. A wave of tension, 
which becomes less as its distance from the center increases, progresses 
outward to the farthest confines of the ball. When the gas contracts, 
a wave of contraction, also starting from the center, and decreasing 
with its distance from the center, progresses outward to the farthest 


confines of the ball. If expansion and contraction are equal the 
ball's former state of equilibrium is restored. 

In this way it can be imagined that starting a current produces 
a state of strain or stretches in the ether in one direction; stopping 
it releases the strain. Action in both cases starts at the point where 
the current is produced and progresses outward with. the speed of 
light, and a little consideration will show that it can have no limit, 
though it soon ceases to be perceptible except under certain condi- 
tions, to be later described. 

The function of wireless telegraphy is to produce these ether move- 
ments at will. 


49. We can produce momentary currents in conductors, whether 
open or closed, by the cutting of lines of force, and the evidences of 
electrification are. most pronounced at the ends of an open conductor, 
but these disappear as soon as th.^ cutting of lines of force ceases. 
We find, however, that electrification of amber, glass, silk, and other 
bodicvs remains after the rubl)ing ceases, and if glass plates or other 
nonconductors be connected to the ends of a conductor in which an 
K. M. F. is being generated, so that connection is made all over the 
surface of the glass (as it is when rubbed), the glass when separated 
from the conductor will be found to be electrically charged the same 
as when electrified by rubbing. When two plates oppositely charged 
(par. 1) are connected through wires leading to a galvanometer, the 
amount of defiection of the galvanometer needle (caused by the mag- 
netic field of the momentary current created as the charges unite 
and neutralize each other) is a measure of the quantity of electricity 
on each ])late. 

In testing plates of different sizes, shapes, and materials, charged 
to the saffie potential by being connected to the poles of the same 
source of electricity, it is found that different values of the throw of 
the galvanometer needle are produced. Other conditions being equal, 
plates having the greatest amount of surface are found to have the 
largest capacity. Plates of the same capacity will give a larger 
throw of the galvanometer when charged from a source of high than 
a source of low potential, so that the amount of electricity stored in 
an electrified body depends on its potential as well as on its capacity, 

50. If two plates, oppositely charged by being connected to the 
poles of a battery, as in fig. 22, are discharged by being connected 
through a galvanometer, the throw of the galvanometer will not be 
as great as if the same plates, charged to the same potential by the 
same battery as in fig. 22a, are discharged through the same galvano- 
meter. By being brought closer together the plates seem to have 
their capacity increased. It takes a greater amount of electricity to 


Virility them t6 the same potential than when farther apart. If two 
plates charged at a distance from each other, as in fg. 22, and then 
disconnected from the battery are brought to the position shown in 
fig. 22a, their potential as measured l)y an electroscope, Ls found to be 
lowered. The electricity is said to be condensed by the approach 
of the plates, and such an arrangement is. termed a condenser^ a 
somewhat misleading term, but one generally used. 

This is analogous to the increased strength of magnetic field pro- 
duced by shortening the magnetic circuit while retaining tlie same 
magnetizing force. In both cases the field of force represents stored 
onerg;^' which can be made to reappear in the discharge of the con- 
denser or the dissipation of the field. 

The two plates can be reduced to one if of nonconducting mate- 
rial, but since a nonconductor can not transmit electric charges, in 
order to utilize the two surfaces of the plate, each must be covered 
with a conductor which will permit the charges to distribute the'm- 
selves over its area. 


61. Electric lines of force permeate a nonconductor — i. e., electric 
induction takes place through it in a way analogous to that in 
which magnetic induction takes place through iron or air. 

Tlie permeability of air for magnetic induction is taken as a stand- 
ard and called unity. (See par. 24.) 

In the same way its permeability for electric induction is taken 
as a standard and called unity, and as we find that iron, nickel, 
cobalt, and oxygen have a greater magnetic permeability than air, 
so we find that glass, beeswax, paraffin, nearh' all kinds of oil, and 
indeed most bodies which we call insulators, have a greater electric 
permeability than air. The quality of a body as compared with air 
in this respect is called its specific inductive capacity, and bodies 
when considered with reference to electric induction tlirough them 
are called dielectrics. 

It is found that the best quality of glass has nine times the spe- 
cific inductive capacity of air. This means that when subjected to 
the same potential, the electric field, when glass Ls the dielectric, is 
nine times as strong as that created when the medium intervening 
between the charges is air, and it req lires nine times as much work 
to create it. 

62. Bodies such as iron or nickel through which magnetic induc- 
tion is taking place are found to change slightly in shape, and sud- 
den changes in the induction or lines of force permeating them 
produce slight sounds. The action is also accompanied by the 
production of heat, but as the magnetizing force (magneto-motive 
force) increases, .the lines of force tend to reach a maximum which 


no increase of magnetic force will increase. • When in this condition 
the magnetized body is said to be saturated. 

In the same way bodies (dielectrics) through which electric induc- 
tion is taking place are found to change (enlarge) slightly in shape, 
but increase of electro-motive force does not appear to tend to a 
maximum of electric induction. The physical strain on the dielec- 
tric, however, continues to increase and finally reaches a point where 
it pierces or ruptures the dielectric, the action being ac<!ompanied 
by a sharp crackling sound and by the production of light and heat, 
which we call an electric spark. If the dielectric is air or a liquid, 
the rupture is immediately repaired by the action of the surround- 
ing substance on that heated by the passage of the spark; but if 
the dielectric is a solid the rupture is permanent. Magnetization is 
limited by saturation. The limit of electrification is marked by 
rupture. The electric charges are found to have been dissipated 
after the spark has passed. The condenser is said to be discharged. 
If the oppositely charged plates are discharged without sparking, a 
slight soimd is produced if the dielectric is glass. This is analogous 
to. the minute sounds given out by magnets when, magnetized or 
demagnetized suddenly. 

We have seen that the capacity of an electrified body depends on 
the area of its electrified surface, on the nearness of its charge to 
charges of opposite sign, and on the material of the dielectric — i. e., 
the substance intervening between the chaTges.r 


53. Bodies capable of being electrified and arranged so as to present 
a large capacity in a small space are frequently called simply capaci- 
ties^ but this term is misleading, and though the term condenser is not 
entirely satisfactory it will be used. The total charge in a condenser 
depends on its potential as well as its capacity. Its potential depends 
on the potential of the source of electricity only, but its capacity, as 
stated above, depends on its size, material, and arrangement. 

54. Condenser capacities may be said to be related to each other in 
the same way as rubber bags inflated by gas. A large bag charged to 
a given pressure contains more gas than a small bag charged to the 
same pressure. The gas in the large bag is making no greater effort 
to escape per square inch (i. e., has no higher potential) than the gas 
in the small bag; but it requires a longer time and more gas to charge 
the large bag than the small one. 

So when connected to the same source of electricity it requires a 
longer time to charge a condenser of large capacity to a given poten- 
tial than it does to charge a small one to the same potential, and its 
power to do work is correspondingly greatei* 


In the same way it requires a longer time to create the magnetic 
field of a large electro-magnet than that of a small one, and Or stronger 
field (within limits) is created by a large current than hy a small one 
under the same conditicms, and the energy stored in the strong field 
and its power to do work Ls correspondingly greater. 

55. It is evident that a close analogy can be drawn between the 
electric field in a condenser and the magnetic field around an electro- 
magnet. We have seen that any movement of either field creates 
the other; that they can exist independently only in a static condition; 
that, though they have no limits, the center of effort, the point of 
greatest activity in each, is at the body which we consider electrified 
or magnetized ; that bodies differ in their qualities in these respects ; that 
an actual physical change takes place in the dielectric when electrified 
and in the iron or nickel when magnetized, and, finally, that both elec- 
tric and magnetic fields represent stored energy in an infinitely elastic 
medium, and we shall see that this medium, on account of its elasticity, 
vibrates and oscillates when either an electric or a magnetic field is 
suddenly created or destroyed in it. 

56. Condensers are of t^n made up of a large number of interlaced 
plates or films of conducting material, having between them for a 
dielectric larger pieces of glass, mica, or oiled paper, and are repre- 
sented either as in fig. 23 or fig. 23a, alternate plates being similarly 
charged. This arrangement fulfills the requirements of surface and 
nearness of opposite charges with intervening dielectric. C(mdensers 
will be represented in this book as in fig. 23. Condensers are also 
made in which the relative position of the plates, and therefore the 
capacity, can be varied at will. These are called variable condensers ^ 
and will be represented as in fig. 23b. In variable condensers the 
dielectric may be glass, air, oil, or mica. The most common and best 
known form of condenser is the Leyden jar, which consists of an inner 
and outer coating or film of tin foil on a glass jar, the glass being the 
dielectric. A photograph of a Leyden jar is shown in PI. 1. Electric 
induction takes place through the glass and the energy is stored in the 
electric field, the tin foil merely serving to increase the area over 
which electric induction takes {)lace, and hence the capacity of the 


57. If, after being charged by connecting the inner coating to one 
pole of a source of electricity and the outer coating to the other, the 
two coatings are connected by means of a conducting wire the charges 
neutralize each other and the condenser is said to be di^scharged. The 
discharge of a condenser being a movement of electricity creates a 
current and consequently a magnetic field around the \vire through 
which the discharge takes place. 


If the potential is high enough the condenser can be discharged 
without actually connecting the two coatings, for when the opposite 
ends of wires connected to them are brought within a certam distance 
of each other sparks will pass, and the condenser will be found to be dis- 
charged, the same as if the wires were actually connected. The charges 
unite by nipturing the air dielectric. The energj' stored in the 
electric field appears as sound, light, heat, and other invisible ether 

This spark discharge is found when analyzed to consist usually of 
several sparks, passing first in one direction, then in the other. Each 
condonser coating is charged positively and negative^ in rapid suc- 
cession, each charge being somewhat less than the preceding until 
the entire energy of the original charge is dissipated. This form of 
condenser discharge is oscillating. The released charge acts like a 
released nmsical string which vibrates until its energy is dissipated, 
and as the same string gives out the same note, whether s^jrettrhrd 
/ Ar.. ♦ strongly or only a little, so a condenser when discharged through the 
same wire always vibrates or oscillates in the same period, regardless of 
its potential. Just as the note given out by the string depends on its 
material and length, so the rate of vibration of a condenser depends on 
its capacity, which, as we have seen, depends on its material and 

68. iinother illustration of oscillatory condenser action can be 
given : Let fig. 24 represent two glass vessels connected by a U tube 
with a stopcock at the bottom of the tube. One vessel is filed with 
water and the other empty. If the U tube is large enough to permit 
free passage of tlie water, when the stopcock is opened quickly tlie 
pressure in the filled vessel will cause a sudden rush of water up the 
other side of the tube into the empty vessel, which will continue until 
it has reached nearly the same height as before (fig. 24a). It will then 
rush back into the first vessel, and so on, reaching a little lower level 
each time until equilibrium is reached at the same level in both vessels 
(fig. 24b). 

The only action wliich i)revents the oscillation from being continu- 
ous is fricti(m of the water on the walls of the tube and internal friction 
between its molecules. 

Released condenser charges would also continue to oscillate indefi- 
nitely if it were not for the friction in the discharging wires and in the 
dielectric and the sound and liglit produced by the spark. These 
absorb the energy of the charge, and, being relatively large, a position 
of equilibrium is reached after a few oscillations. 

If the U tube in fig. 24 is very small or the stopcock only slightly 
opened the water will gradually rise on the other side and will finally 
reach a position of equilibrium without any oscillation, and it is foimd 
that if the condenser discharge takes place through a long thin wire 


instead of a thick one the condenser is slowly discharged throut]:h it 
without any oscillation. 

59. The oscillation of the water in fi^. 24 is due to its inerfui. Inertia 
is a property of all bodies and is in amount proportional to their 
weiorht. It is represented by their resistance to change of condition, 
either of motion or of rest. 

The water in the first vessel fallft by the action of gravity. ()nc(^ in 
motion its inertia (resistance to chano^o of condition) causes it to rise 
on the opposite side against the action of gravity. When gravity has 
overcome its inertia it falls again by gravity and is carried on by 
inertia. It continues to overshoot the mark, so to speak, until friction, 
internal and external, brings it to rest. 

Though the electric charges on condenser coatings appear to be inde- 
pendent of gravity, they do possess inertmy as is shown by their resist- 
ance to change of direction (par. 103) and by their oscillatory 

60. Let us consider a charged condenser (fig. 25) discharged through 
a thick wire connecting the coatings. A break in the wire prevents 
tlie discharge until the potential is high enough to cause sparks to 
cross the break. One condenser coating before discharge is at a cer- 
tain positiv^e potential, the other at an equal negative potential. Both 
discharge through the wire in the same time, and when they have 
reached zero potential the electric field has been dissipated, but the 
moving charges in the wires have induced a magnetic field around the 
wire. The strength of this magnetic field depends on the amount of 
the moving charges, i.e., tlic strength of the current, and on the self- 
induction (par. 28) of the wire which, as we know, depends on its 
shape and the material (air or iron) in which the magnetic field is cre- 
ated. All the energy (except that lost by friction) which was stored 
in the electric field is now in the magnetic field (fig. 2oa). The mag- 
netic field having no continuous source of magneto-motive force (cur- 
rent) to maintain it collapses on the wire, j)roducing movements of the 
electric charges into the comienser coatings, which now become 
charged in the opposite sense (fig. 25b). The electric field is again set 
up, containing all the remaining energy", and the magnetic field disap- 
pears until the charges again move toward each other. 

The attraction of the unlike charges for each other Ls analogous to 
the attraction of gravity in the water in fig. 24, and the magnetic field 
caused by the self-induction of the moving charges is analogous to the 
inertia of the water, which makes it rise in the second vessel, because 
the collapse of this magnetic field charges the condenser in the oppo- 
site sense, and for this reason self-induction is sometimes called electro- 
magnetic inertia. 

From the foregoing illustration of what appears to take place during 
the oscillating discharge of a ct)ndenser we see that the energ}" before 


an oscillation begins is all electric. At the end of the first quarter of a 
cycle it is all magnetic. At the end of a half cycle it is all electric, but 
in the opposite sense. At the end of three-quarters of a cycle it is all 
magnetic, but with the direction of the lines of force reversed. At the 
end of a complete cycle or oscillation the energy is all electric again 
<figs. 25a, 25b, 25c, 25d) and in the original sense, but less in amount 
on account of the losses which have taken place during the transforma- 
tions and which are shown by the heating of the wires of the condenser 
(and the sound and light produced by the spark if the oscillations take 
place through a spark gap). At all intermediate points of a cycle the 
energy is partly electric and partly magnetic. 

61. A complete oscillation or cycle is made up of two alternations. 
The highest potential reached during an oscillation is called the ampli- 
tude of the oscillation. The difference between the amplitude of two 
successive oscillations is called the damping and is a measure of the 
losses. The interval in time between two successive oscillations is 
called the period. 

62. Since every body has electric capacity in proportion to its sur- 
face (par. 52), and since movements of electric charges without which 
a body can not be electrified, always produce magnetic fields, every 
body must have self-induction, and therefore electro-magnetic oscilla- 
tions can take place in it. 

We know that every body vibrates in its own period mechanically, 
and we find that every body vibrates in its owti period electrically, and 
further that the number of vibrations or oscillations per second 
depends entirely on the capacity and self-induction of the body. 

It will be seen that while a closed circuit is necessary for the flow of 
a continuous or direct current, for oscillating currents a straight wire 
is sufficient. A circuit containing a condenser which would com- 
pletely obstruct a direct current has no effect on an alternating ciir- 
reit other than to change its sign. '' 

63. We must be careful to distinguish between the capacity of a 
condenser and the total charge in it, and between the self-induction of 
a wire and the total induction caused by the current in it. The 
capacity J it may be repeated again, depends on the material and ar- 
rai^gement of the charged body. The total charge — that is, the total 
electric induction — depends on the capacity and the potential. In 
like maimer the self-induction depends on the arrangement of the 
conductor and the suiTounding material (whether iron or air). The 
total magnetic induction depends on the self-induction and the 

64. We can see in a general way why the period of an oscillating 
circuit depends on the capacity and self-induction of the circuit, and 
not on the total electric or total magnetic induction, because the 
capacity and self-induction are determined by the material and 


arrangement of the circuit, which qualities determine the mechanical 
period of a body. It takes longer to discharge a condenser of large 
capacity than one of small capacity, and it takes longer to create a 
given current in a circuit of large than in one of small self-induction. 
Increasing the potential gives more work to be done during a dis- 
charge, but also gives power to do it in the same ratio, so that mcrease 
of potential does not change the period, though it may change the 
ampUtude of the oscillations. 

66. It was stated (par. 29) that coiling a wire increases its self- 
induction and enables a strong magnetic field to be created around it, 
and that this increases the electrical length of the ware — i. e., it takes an 
electrical disturbance started at ore end of it longer to reach the other 
end when the wire is coiled than when the same wire is straight. 

Now we see that the electrical length of a wire depends on its 
capacity and self-induction and that its period in seconds — i. e., the 
time of one complete oscillation (the time required for an electrical 
impulse started at one end to reach the other and be reflected back) — 
must be twace its electrical lergth divided by the velocity of elec- 
tricity, which we know to be that of light, or 300,000,000 meters per 
second, and the number of complete oscillations per second is the 
reciprocal of its period. 

The capacity and inductance of a straight wire long in proportion to 
its thickness are so related that its electrical length is equal to its 
natural length. 

From the above the period or time of one complete electrical oscilla- 
tion of a straight wire one meter long is jaTrcj^fir^TJo second, and it 
therefore oscillates 150,000,000 times per second. 

The number of oscillations or cycles made by an alternating current 
per second is called its frequency. 

66a. We know that by coiling a wire its self-induction can be 
greatly increased, and its period thereby lengthened. By adding 
capacity to the wire in the shape of condensers its period can be 
lengthened still more, so that by suitable arrangements a current hav- 
ing small mechanical length, but comparatively great electrical 
length, can be made up in a small space. 

Such a circuit is shown in fig. 26. It is made up of a condenser 
connected to a coiled wire, and will be called in this book an oscillating 

The oscillating circuit in fig. 26 may have a break or gap in it, as in 
fig. 26a. If the potential of the condenser is sufficient to rupture the 
air or other dielectric in the gap, the circuit does not lose its oscillating 
character. The presence of the gap does, however, decrease the num- 

A'. B. — It must not be forgotten that every wire possesses capacity by virtue of its 
surface and self-induction by virtue of the fact that an electric airrent can flow in it. 
Even condensers have a certain amount of self-induction. 
2740—06 3 


her of oscillations for one charge and prevents the complete discharge 
of the condenser, because the oscillations cease as soon as the poten- 
tial falls below that necessary to rupture the gap. The greater the 
loss or damping in each oscillation the smaller the number of oscilla- 
tions that will take place before the potential falls so low that it ^-ill 
ncFl^upture the spark gap. 

66. As stated in paragraph 52, the term condenser is not satisfac- 
torj'^, and the word copocity is often used to mean conrf^n^^r, especially 
in connection with such an oscillating circuit, the condenser being 
spoken of as a capacity and the coiled wire as an inductance, which 
means a conducting wire arranged so as to have large self-induction. 

Fig. 27 represents an indu4:tive resistance, or simply an inductance, 
since it is assimied that all wires have resistance. 

Fig. 27a represents a noninductive resistance, the uses of which will 
be explained later. 

An oscillating circuit whose electrical length can be varied at will is 
represented in fig. 28. It consists of a variable condenser in connec- 
tion with a fixed inductance, fig. 28, or it may consist of a fixed con- 
denser and a variable inductance, fig. 28a, or both capacity and 
inductance may be variable, the arrow in fig. 28a being meant to show 
that any number of turns of the coil can be included at will. 

67. Two circuits having the same electrical length are said to oscil- 
late in resonance; their periods are equal, though the inductance and 
capacity may not bo the same in each. Oscillating circuits now used 
in wireless telegraphy have electrical lengths varying from 100 to 1,500 
meters, giving from 1,500,000 to 100,000 oscillations per second. 
Those first used by Marconi had electrical lengths of about 12 centi- 
meters and oscillated approximately 2,500,000,000 times per second. 


68. As stated in paragraph 60, a cycle is made up of two altema- 
ticms or movements in opposite directions and is represented in fig. 18. 
Such a curve also represents the crest, hollow, and slope of regular 
waves on the surface of the ocean or Otlier body of water. The dis- 
tance from crest to crest or from hollow to hollow of a water wave is 
culled a wave length, and this distance is equal to that of two alterna- 
tions. Since electro-magnetic (ether) disturbances spread in all direc- 
tions with the speed of light, and when sent out by an oscillating cir- 
cuit succeed each other at equal intervals of time, and since the lines 
of magnetic and electric force in oscillating circuits change direction 
during each alternation, just as the particles of water rise to the crest 
or fall to the hollow of a wave, the positive and negative amplitudes 
may represent the crests and hollows of waves separated by half 
periods or half waves length, an oscillating circuit may be called a 
wave {)roducer, and the oscillations considered as moving tlirough the 
ether may be called ether waves. 


69. The vibrations of particles producing sound waves, as in air, 
consist of to-and-fro movements parallel to the direction of the waves, 
the latter consisting of alternating conditions of compression and 
rarefaction of the air. 

The movement of the particles in ether waves is at right anglCvS to 
the direction of propagation of the wave, and the electric and magnetic 
movements are also at right angles to each other at any point in the 
wave front. This is called transversal vibration, as distinguished 
from the longitudinal vibration of the particles in sound waves. 

When one particle of a substance is displaced or made to vibrate, it 
induces its neighbors to follow it, and starts them to vibrating in the 
same periods but in different phases, each particle starting to vibrate 
(passing the word, so to speak) at a definite interval of time after the 
one next to it has started. The vibrations may be longitudinal or 
transverse, as described above, or they may be circular or elliptical, 
but if they are regular the waves produced are regular. 

The amplitude of the wave (par. 61) depends on the extreme limits 
from its normal position of the vibration of each individual particle. 
The wave length depends on the time of one complete vibration of each 
particle and the velocity with which the displacement or vibration is 
propagated from one particle to another of the substance. It is found 
that this velocity is equal to the square root of the elasticity of the 
body divided by its density. 

We know that this velocity in the ether is 300,000,000 meters per 
second, and we conclude that the ether must have very great elas- 
ticity combined with very small density. 

It has been stated that electric charges or electrons are the only 
things which have a grip on the ether, and that when they are vibrat- 
ing the ether vibrates with them. 

When a particle is subject to several forces at the same time, its 
resultant movement depends on the resultant of the forces and will 
vary as the forces vary, so that a body can, in effect, vibrate in more . 
than one way at the same time, and can produce complex waves where 
vibrations are superimposed on each other. This is shown every day 
at sea by the small waves or ripples on the slopes of larger ones, or 
the short waves from local winds superimposed and propagated in the 
same or different directions from the long swells due to distant storms. 

The vibrations producing ether waves, and consequently the wave 
lengths and frequenpies, are of an almost infinite range, for instance: 

Ether vibrations from 430 to 740 trillions per second (a little less 
than one octave) are visible to the eye and are called light. 

Between 870 and 1,500 trillions of vibrations per second we have 
the ultraviolet and X rays, and from 430 down to 300 trillions of 
vibrations .per second the infrarouge rays. 


Below 300 and down to 20 trillions of vibrations per second we 
detect ether vibrations by our sense of feeling or by the thermometer, 
and they are called heat 

Forty-five octaves lower on the same scale are the ether vibrations, 
which we call electric waves and which are used in wireless telegraphy. 
The shortest of these yet measured is 0.2 of an inch in length; the 
longest, over 1,000,000 miles. 

Marconi, in his first experiments, used a pair of small spark balls 
which gave out waves about 12 centimeters in length. 

Ether waves of all lengths are subject to reflexion, refraction, dif- 
fraction, and absorption, and bodies, sqch as insulators of certain 
lands, which are opaque .to the short waves we call light, are trans- 
parent to the long electric waves used in wireless telegraphy. Prac- 
tically all conductors are opaque to electric waves. Generally speak- 
ing, insulators are transparent to electric waves, but in transmitting 
the wave thev absorb some of its energy. 

Conductors being opaque to electric waves partially reflect and 
partially absorb the wave energy. 

A simple case of wave reflexion is seen when a rope hanging verti- 
cally is given a quick jerk and then held taut in the hand. A wave 
can be seen traveling up the rope till it reaches the top, where it is 
reflected, travels do^^n the rope to the hand, is reflected there and 
starts up again to the top, and so continues until its energy is damped 

If a number of equally timed jerks are given, a succession of waves 
at equal intervals is sent up the rope. When reflected back they 
meet others coming up whose lengths are equal to those coming down. 
At some points the rope tends to move a certain distance in one direc- 
tion with the direct wave, and the same distance in the opposite direc- 
tion with the reflected wave, the result is that it does not move at all. 
These points are found along the rope one-half wave length apart; at 
all other points the rope moves or vibrates in the resultant direction 
of the direct and reflected wave impulses, and what are called station- 
ary waves are set up. 

The points at which there is no movement are called nodeSj and 
points at which there is maximum movement are called loops. This 
is shown graphically in fig. 18e. 

Stationary ether waves can be set up around conducting wires by 
suitably timed electrical impulses applied to the ends of the wires. 

It will be observed that the point of support of the rope where it 
can not move must, in every case, be a node. So in a conducting wire, 
the end of the wire away from that receiving the impulses must be a 
current node, because no current can flow there. It can, however, and 
a Uttle consideration will show that it must, be a potential loop, for 


while there is no movement at the point of support, the greatest pres- 
sure or tendency to move is there. 

Since the electrical impulses consist of variations of current and 
potential, which succeed each other regularly, and since at a given point 
we find a loop of potential and a node of current, we must, at a quarter- 
wave length distant, find a node of potential and a loop of current. 

This is shown graphically in fig. 18f, which represeiits the relative 
positions of current and potential nodes and loops in stationary elec- 
tric waves, and illustrates the statements made in paragraph 60 (figs. 
2.5a, etc.), relative to the alternations of electric and magnetic fields in 
oscillating condenser discharges. 

If an oscillating current be set up in a free wire (fig. 18d) by a neigh- 
boring discharging circuit in resonance with it, this wire will be found 
by measurement with a micrometer spark gap to have an alternating 
potential in it, varying from nothing at the middle point, C, to a maxi- 
mum at either end somewhat similar to the full curve E C F. 

If at the same time the current in the wire could be measured, it 
would be found to have a maximum value at C and a minimum at the 
ends similar to the dotted curve A D B. If the wire A C B is not too 
far from the discharging resonant circuit and the wire be cut at C and 
an incandescent lamp L be connected to the two halves as shown in 
the figure, the lamp will glow. 


69a. If ether waves impinge on a reflecting surface not normal to 
their direction, they are reflected at an angle equal to that which 
the reflecting surface makes \vith their original direction (the angle of 
incidence is equal to the angle of reflection), so that directed waves 
may be detected at points not in the line of direction by the interpo- 
sition of a reflector. 

Air at atmospheric pressure (about 760 millimeters of mercury) is 
an insulator. Its pressure decreases with distance above the earth's 
surface, and its insulating qualities decrease with the decrease of pres- 
sure. At a height of approximately 45 miles above the earth's sur- 
face its pressure is about 1 millimeter of mercury. At this pressure it 
is a good conductor, and though still transparent to short ether waves 
like those of light, it partly reflects and partly absorbs long ether 
waves. In the intermediate distance it is at first transparent, then 
partially transparent, absorbent, and reflecting, simultaneously. 

It is known that ether waves are guided by conducting surfaces to 
a certain extent (for instance, by wires), as well as reflected by them, 
and that otherwise they travel in straight lines. Fig. 18g shows the 
approximate path of an ether wave started from the earth's surface 
and reflected from the upper atmosphere. It will be seen that even 


if the earth's surface did not guide the waves they might be detected 
at points below the horizon. 

Other causes of reflection may exist, such as large bodies of electri- 
fied air, or heavily charged clouds, which would cause interference 
between direct and reflected waves and make electrical shadows at 
certain places, i. e., points at which, owing to conditions outlined 
above, either the waves are so attenuated that they can not be detected 
or they are completely neutrahzed. 


69b. When ether waves impinge on transparent bodies at any angle 
other than the normal, if their velocity in the transparent body, on 
account of its elasticity or density, is different from that at which they 
were previously moving, that part of the wave first entering the body 
will move either faster or slower than it did before. The part outside 
will therefore either gain on it or fall behind it. This action will affect 
each portion of the wave fi'ont as it enters the body, and the result 
will be that its direction of movement will be changed. The effect 
is to bend the wave out of its original path, and the action is called 

Ether waves passing through the atmosphere, whose density varies 
at different points, are subject to this bending action. 


69c. When waves meet a body in their path (for instance, when 
the comparatively long waves used in wireless telegraphy impinge 
on a high island or mountain range) at the points where the wave 
front cuts the extreme width of the island new c^nt;ers of disturb- 
ance are created, which radiate some of the wave energy to points 
behind the island. It has the effect of bending the waves around 
the object. This action also takes place at the summit, as well as 
at the water's edge. This action of waves is called diffraction. In 
amount it depends on the wave length. From the new centers of 
disturbance waves are sent out, which interfere with each other, not 
being propagated in the same directions. The result is that for a 
distance, depending on the width and height of the obstacle and on 
the wave length, a shadow exists bey(md it. 

Partial reflexion of the waves toward their source takes place on 
the side of the obstacle nearest the source. An attempt to show 
this graphically is made in fig. 18h, but the best illustration is given 
by the motion of water around a rock on a windy day. The small 
back waves on the windward side are reflected to windward. The 
waves circling or bending around the rock are diffracted. The still 
water in the lee of the rock is the shadow, in which no action exists. 


At a distance depending on the size of the rock and the wave length 
the zoneis of interference disappear, the regular waves from the two 
sides of the rock unite, and there is no evidence of its existence at 
points beyond, though it has decreased the total strength of the 

For the above* reasons high land between two wireless telegraph 
stations has the effect of decreasing the strength of signals at each 
station, and if close to either station may entirely prevent that sta- 
tion from receiving. (It may be in the shadow or be subject to 
interference from reflexion.) 

The effects of reflexion and diffraction on waves passing over 
irregular country are very pronounced. The effects of reflexion, 
refraction, and absorption in the atmosphere are equally pro- 
nounced, the qualities of the atmosphere in all three respects vary- 
ing greatly from day to day and between day and night. 

An ether wave traveling from one wireless-telegraph station to 
another over rough country and through an atmosphere of var^ang 
density, working its way around and over mountains, being bal- 
lotted from thunder clouds at one point and absorbed by semicon- 
ducting gases at another, may be said to pursue an adventurous 

70. We have now seen how to produce electric and magnetic 
fields, how to utilize magnetic fields for the production of electric 
currents in dynamos, how to increase the potential of these currents 
by means of step-up transformers, and how by means of this high 
potential current to force large charges into electric accumulators or 
condensers and by discharging these condensers in oscillating cir- 
cuits to produce what we call electric or ether waves. These opera- 
tions can be represented graphically or diagrammatically, as in fig. 
29, which shows a separately excited A. C. dynamo in circuit with 
the primary winding of a step-up transformerj whose secondary 
charges the condenser of an oscillating circuit containing a spark gap. 

The secondary winding of the transformer is very long, in order to- 
give a high potential. The transformer also has an iron core. The 
great number of turns of the secondary winding, added to the effect 
produced by the iron core, gives the circuit containing the secondary 
winding and the condenser a very large self-mduction, and conse- 
quently a veiy long period. The circuit composed of the condenser, 
self-induction, and spark gap has a very much shorter period, and 
when the spark gap is ruptured it oscillates as if it were entirely 
disconnected from the secondary, usually completing its oscillations 
and coming to rest in a fraction of the period of the circuit formed 
by the secondary winding and condenser. 

The oscillating circuit (condenser, spark gap, and inductance) is 
shown in fig. 29 near a conducting wire, having a few turns of 


inductance close to those of the oscillating circuit. In this circuit 
we can consider the condenser as representing the source of cur- 
rent, like the battery in fig. 11, paragraph 12; the spark gap as the 
break K, the turns of inductance in the oscillating circuit as A B, and 
the open circuit with one end grounded as C D. The oscillating cur- 
rents in A B produce like currents, but in the opposite direction in 
C D (par. 12), and C D becomes a source of ether waves. 

The production of ether waves and their detection at a distance 
fi'om the source constitutes wireless telegraphy. 

C D is usually called the open or radiating circuit. 

A B the dosed or oscillating circuit. 

The two inductances form the primary and secondary, respec- 
tively, of an air-core transformer (par. 26). When arranged as in 
fig. 29, A B and C D are said to be inductively connected. 

C D may have part of its inductance common to A B. The 
aiTangement in this case acts as an autotransformer (fig. 14d) and 
A B and C D are said to be direct connected. 

If the oscillating and radiating circuits have the same period, they 
oscillate or vibrate in resonance. The radiating circuit in such a 
case receives the inductive impulses from the oscillating circuit at 
the proper time, and the amplitude of its oscillations are thereby 

The adjustment of A B and C D to any given period and their 
adjustment to each other's periods is called tuning. 

It will be noted that the oscillating circuit has concentrated capac- 
ity , while the capacity of the radiating circuit is distributed. 

71. The fundamental principle of wireless telegraphy is that all 
bodies vibrate electrically as well as mechanically ; that their periods 
of electrical vibration depend solely on the capacity and self^nduc- 
tion of the vibrating body; that these electrical vibrations produce 
ether waves, which are propagated with the speed of light, and which 
can be detected at great distances from their source by means of 
instruments specially designed for the purpose. 

Chapter 11. 


72. Attention has thus far been concentrated on the qualitii 
rather than the quantity of the electro-magnetic actions under dis- 
cussion. Before proceeding further it is necessary to consider the 
standards of measurement adopted and their relation to each other. 

73. Electric and magnetic actions being forms of energy, and being 
mutually convertible, as we have seen, are subject to all the laws gov- 
erning transformations of energy. 

Work is done when conductors are moved in magnetic fields, the 
resistance to movement and the amount of movement determining 
the amount of work done. 

The unit of mechanical worTc is a foot-poundy by which name we 
designate the work done in lifting 1 pound 1 foot against the 
action or farce of gravitj^. 

Force, by which we mean the cause of action or movement (pull- 
ing or pushing ability), is measured in pounds, and /orc€ multiplied 
by the distance through which it acts is work. Lifting 10 pounds 10 
feet =100 foot-pounds. 

The amount of work done in a given time — that is, the rate of doing 
work — is called power. The unit of mechanical power we call a horse- 
power, and it represents a rate of doing work equal to 33,000 foot- 
pounds per minute: * 

In the above definitions of work and power the units of distance j 
weight (or mass) and timej used are the /oo<, pound j and minute, all of 
which are defined by law and are called fundamenMl units. 

74. Another system of units, proposed by the British Association 
for the Advancement of Science and now generally used in electrical 
measurements, is based on the centimeter^ gram, and second^ and is 
usually called the c. g. s. system. The use of this system is author- 
ized by law. 

The following relations exist between the two sets of units: 
1 foot = 30.48 centimeters, approximately. 
1 pound =453.59 grams, approximately. 
1 minute = 60 seconds. 
The unit oi force in the c. g. s. system is that force which acting on a 
gram mass for 1 second gives it a velocity of 1 centimeter per second. 
This force is called a dyne, 

• 41 


The imit of work in the c. g. s. system is the work done, in over- 
coming the force of 1 dyne through 1 centimeter and is called an erg. 

The force of gravity acting on a gram mass for 1 second will give 
it a velocity of 32.2 feet per second = approximately 981 centimeters 
per second; therefore the force of gravity is equal to 981 dynes and 
the pull of a dyne represented as a weight is equal to ^jj^ of a gram. 

The pull of a pound, which equals 453.59 grams, must be equal to 
that of 453.59X981 = approximately 445,000 dynes. 

An erg by definition is a dyne overcome through a centimeter, and a 
foot-pound is 453.59X981 dynes overcome through 30.48 centimeters: 
therefore di foot-pound equals 453.59X981 X 30.48 = approximately 
13,570,000 ergs, and a horse power, which equals 550 foot pounds, 
per second = 453.59 X 981 X 30.48 X 550 = approximately 7,460,000,000 
ergs per second. 

76. On account of the fact that the names adopted for the prac- 
tical electro-magnetic units are all names of notedscientists and not 
related to nor in any way descriptive of the qualities they are used 
to designate, their acquirement must be entirely a feat of memor>'. 
They can be more easily remembered by associating them with the 
names of the theoretical or absolute units. 

The absolute units used in electrical measurements are those of 
electro-motive force, current, and resistance. They are defined in 
terms of the c. g. s. system. 

76. The flow of electric current in any conductor is found to be 
governed by the tendency to flow (the electro-motive force) and 
the resistance of the conductor. 

The resistance is found to be governed by the material, size, and 
length of the conductor. 

An electric current generated by moving a conductor in a mag- 
netic field creates its own magnetic field around the conductor. The 
stronger the current, the stronger its magnetic field, and the greater the 
reactive effect or pull on the conductor in which the current is flow- 
ing, and consequently the greater the amount of work necessary to 
keep the conductor moving across the lines of force. 

The E. M. F., which causes the current, depends on rate of cutting 
or rate of movement. The force opposing this movement depends 
on the current flowing, and this again on the resistance of the circuit. 

Magnetic fields are represented in strength by the number of lines 
of force per square centimeter that they contain. 

Unit magnetic field is said to contain one line of force per square 
centimeter (the field, of course, being uniform throughout), and is 
such a field as will act on unit magnetic pole with a force of 1 dyne. 
Unit pole being such a pole as will, when placed at a distance of 1 
centimeter in air from a similar pole of equal strength, be repelled 
by a force of 1 dyne. 



Moving a conductor across unit field so that it cuts 1 square 
centimeter of the field per second generates unit E. M. F. 

If the conductor forms part of a closed circuit and the current gen- 
erated in it is such that when cutting 1 square centimeter of unit field 
per second its movement is opposed by a force of 1 d^axe, the circuit is 
said to have unit resistance, unit current is said to flow, and the work 
done is 1 erg per second ( the force of a dyne overcome through a cen- 

If the resistance of the circuit is decreased one-half the current is 
doubled, opposition to movement is also doubled, and consequently 
the work is doubled. In other words, the current varies inversely as 
the resistance and the work done varies (firectly as the current. 

If the rate of movement is increased so that 2 square centimeters 
of the field ( two lines of force) are cut per second the E.M.F. is doubled, 
the current is doubled, the opposition to movement is doubled, and 
consequently the work per second is quadrupled because it represents 
the force of 2 dynes overcome through 2 centimeters in one second. 
This shows that the work done varies with the electro-motive force as 
well as with the current, and the work per second or the power there- 
forjp varies as the product of the E.M.F. and current, since it varies 
directly with each. 

It also shows that the current varies directly with the E. M. F. 

We have seen that it varies inversely as the resistance. 

E. M. F. 
We can state therefore that current = t:> — '~^ (1) and that the 

Kesistance ^ ^ 

the work done in creating the current is equal in ergs per second to 

E. M. F. X current (2). 

By agreement among electricians, electric current is represented by 

the letter /, electro-motive force by the letter E, resistance to the 

flow of electricity by the letter /?, power b}^ the letter jP, work 

bv the letter Tr, time bv the letter T. 

Equation (1) can therefore be written / = » (3) and (2) written 


P= y— /7?(4). 

Equation (3) is the fundamental electrical equation and states in 
mathematical form what is known as Ohm's law, viz: '^The current in 
any circuit varies directly as the electro-motive force, and inversely as 
the resistance in the circuit. '' 

77. Since magnetic fields containing 125,000 Imes of force per 
square centimeter can be obtained, a rate of cutting of one line per 
second gives too small a unit of E. M. F. for practical use. 

On the other hand, the current necessary to produce a resistance of 
1 dyne to this slow movement in unit field Ls somewhat large, and to 
replace the theoretical or absolute units the so-called practical units 
have been adopted. 



Th3 practical unit of E. M. F. is the volt and is the E. M. F. generated 
when Unes of force are cut at the rate of 100,000,000 per second. 


The practical unit of current is the ampere and is one- tenth of the 
theoretical unit. 


In order to maintain the truth of the equation 7=^(3), the prac- 
tical unit of resistance, wliich is the ohm, is taken as 1,000,000,000 
times the theoretical or absolute unit. 

K volts 

Ohm's law then still remains true. ^ = p (3) or amperes = ^u— » 

because this equation in terms of the aboslute units is .^ (amperes) = 

A'X 100,000,000 (volts) u- i • *u t ^/o^ o^i. 

T^ . .^..L ..^!. ^^^ /-I- . , which IS the same as / = „ (3). The s^ize 
R X 1,000,000,000 (ohms)' R 

of the units has been changed but the proportion between them is the 

same as before. 


The practical unit of power is the wait, which is the ergs of work 
done per second when 1 ampere is flowing with an E. M. F. of 1 volt. 

This in ergs (see equation (4)) equals unit E. M. F. X 100,000,000 X 
unit ^'"rrent^ ^^ 10,000,000 ergs per second. Therefore 1 watt equals 

10,000,000 ergs per second, and the power expended in any circuit in 
watts equals the product of the volts and amperes in the circuit, or 
P = A/(4). 

Ten million ergs of work is called a joule. Therefore a watt = l 
joule per second. 

We have seen that 1 H. P. =7,460,000,000 ergs per second. There- 
fore 1 watt = ^.^ H. P. = approximately 0.737 foot-pounds per 


78. After having selected the practical units, it became necessary, 
for the purpose of comparison and for everyday use, to represent 
them in concrete form, because the accurate measurement of dynes 
and ergs is a very difficult matter practically. 

However, b}^ balancing them against known weights, the actual 
pulls produced by currents and the work necessary to create them 
can be determined, and thus the absolute values of the currents and 
E. M. Fs. themselves determined. 

The current from certain primary batteries is found to be con- 
stant when their terminals are connected by the same wire. This 


affords a means of directly comparing the resistances of wires of 
various sizes, lengths, and materials. 

It is also found that the decomposition of an electrolyte (par. 1), 
by an electric, current, always results in the separation or deposit of 
exactly equal quantities of the constituents of the electrolyte ifor 
equal quantities of current. The deposit in a certain time being 
weighed, serves as a ver}^ accurate measurement of the amount of 
electricity which passes in that time, and consequently affords a very 
accurate means of comparing electric currents and determining their 
absolute values. 

The relation between heat and mechanical energy being known, the 
relation between electrical and mechanical energy was practically de- 
termined by measuring the heat produced by electric currents, and the 
absolute values obtained by the methods outlined above were verified. 

79. On account of the relation / = - (3) between amperes, volts, and 

ohms in a circuit, if any two of tliem are known the other is also known, 
so that only two measurements of concrete units are required. The 
question of which two should be selected and the exact form that each 
should take has been the subject for discussion at a number of inter- 
national conferences, the latest of which, held in Berlin in October, 
1005, has recommended that only two electrical units shall be chosen 
as fundamental units, viz, the international ohm defined by the resist- 
ance of a column of mercury and the international ampere defined b}" 
the deposition of silver. 

The volt is defined as the E. M. F. which produces an electric current 
of 1 ampere in a conductor whose resistance is 1 ohm. 

In this conference the ITnited States delegate contended for the volt 
and the ohm as the theoretically independent units, and it is not yet 
certain that these two will not be those finally selected as standards. 

Different methods^ of measurements produce slight differences in the 
values of the standards, but the values recognized by law in the United 
States are as follows: 

The standard ohm is the resistance ofl'ered to an unvarying electric 
current by a column of mercury at the temperature of melting ice — 
14.4521 grams in mass — of a constant cross-sectional area, and of a 
length of 106.3 centimeters. 

The standard ampere is the unvarying current, which when passed 
through a solution of nitrate of silver in water in accordance with cer- 
tain specifications deposits silver at the rate of 0.001118 of a gram per 

As previously stated, a volt is the E. M. F. which if steadily applied 
to a conductor whose resistance is 1 ohm will produce a current of 
1 ampere but a concrete standard for the volt is also recognized by 
law, it being specified: 


That the electrical pressure at a temperature of 15° centigrade 
between the poles or electrodes of the voltaic cell known as Clark's 
cell, prepared [in accordance with certain specifications, may be 
taken as not differing from a pressure of 1 .434 volt-s by more than 1 
part in 1 ,000. 

(A Clark cell consists of zinc, or an amalgam of zinc with mercury-, 
and of mercury in a neutral saturated solution of zinc sulphate and 
mercurous sulphate in water, prepared with mercurous sulphate in 

The latest international conference has recommended the adoption 
of the Weston cadmium cell as preferable to the Clark for a standard 
cell. The Weston cell has an E. M. F. of 1.025 volts. 

(The Weston cadmium cell consists of cadmium amalgam, covered 
with a layer of crystals of cadmium sulphate and pure mercury in^on- 
tact with a paste of mercurous sulphate, cadmium sulphate crystals, 
and metallic mercury, the electrolyte being a concentrated aqueous 
solution of cadmium sulphate and mercurous sulphate.) 

Standard resistance wires having a known ratio to the legal ohm are 
made, and these, with standard cells calibrated by their means and by 
means of the standard ampere, are used for calibrating volt meUrs and 
ammeters, which are the names given to the instruments for indicating 
automatically the E. M. F. and current in any circuit. In this way 
electrical values are made uniform throughout the country. 

80. In addition to the volt, the ampere, the ohm, the watt, and the 
jovle other practical units have been adopted, the most important of 
which, for our purposes, are: 


The unit of quantity, the coulomb, which is the amount of electricity 
passing any point in a second when 1 ampere is flowing in the cir- 


The unit of capacity, the farad. A condenser is said to have a 
capacity of 1 farad when 1 coulomb of electricity will charge it to 
a potential of 1 volt. 

(Potential and E. M. F. are in some senses identical, one being the 
passive and the other the active state. iVn E. M. F. is the result of 
difference of potential.) 


The unit of self-induction, the henry. A circuit is said to have a self- 
induction of 1 henrj^ when, if the current in it is varied at the rate of 
1 ampeje per second, the induced E. M. F. — that is, the counter 
E. M. F. (par. 89) — tending to oppose the change is 1 volt. 


81. 'While the volt, the ampere, and the ohm are really practical 
iinit^, the farad and henry are not. 

It would take a very large condenser to have a capacity of 1 farad 
and a coil of many turns to have a self-induction of 1 henry. Sub- 
divisions of the farad and henry are in practical use. 

Multiples and subdivisions of the other units are also frequently 
used, and for this purpose the prefixes kilo, meaning 1000; mega, 

meaning 1,000,000; milli, meaning ^ ^^^ and micro, meaning 

l"()0()l)00^ are added to the units, and such terms as — 
kilowatt = 1 ,000 watts, 
megohm = 1 ,000,000 ohms, 

millivolt = . ^^^ volt, 
milliampere =. ^..^^ ampere, 
millihenry = ^ ^^^ hemy^ 

microfarad =i oOO,000 ^^''^^^ 
microsecond = . ^^^ ^^^ second, 

are in common use. In fact, the real practical units of capacity and 
self-induction (the qualities of electric circuits with which wireless 
telegraphy is principally concerned, because they determine the 
period of vibration) are the microfaraa and the millihenry. 

The terms mil, meaning . ^,wx inch; micron, meaning . ..^^ ^^^inch; 

circular mil, meaning area of a wire having a diameter of . ^.w.inch, 

are also in general use among electricians. 

82. The voltage, or E. M. F., in any circuit connected with a dynamo 
depends only on the rate of cutting of lines of force. 

The resistance (ohms) in any circuit depends only on the material, 
cross section, and length of the conductor forming the circuit. 

The current (amperes) in any circuit depends only on the E. M. F. 
and the resistance in the circuit. 

The power (watts) in any circuit depends only on the E. M. F. and 
current in the circuit. 

The self-induction (henrys) in any circuit depends only on the 
.shape and length of the circuit, on the magnetic permeability (par. 24) 
of the material surrounding and inclosed by the circuit, and on the 
amount of this material. 

The capacity (farads) in any circuit depends only on the shape and 
area of its surface, on the electric permeability of the material sur- 


rounding the circuit, on the amount and location of this material (the 
dielectric), and oa the position of the circuit relative to other con- 

(Straight wires are said to have distributed inductance and capacity, 
coiled wires have concentrated inductance, and condensers have con- 
centrated capacity.) 

The coulombs in a charged condenser or circuit depend only on the 
capacity and potential of the condenser or circuit. 

A volt =100,000,000 = 10 » absolute units of E. M. F. 

An ohm = 1,000,000,000 = 10 " absolute units of resistance. 

An ampere = ^\ =10"* absolute units of current. 

A watt= a volt X an amp. =10* X 10"* =10^ absolute units of 
work per second = 1 joule per second =7!^ H. P. =0.737 foot pounds 
per second. 

83. Referring now t^ the definitions of the henry and farad, it is 
evident that they depend on the units of E. M. F. and current. 

If these definitions were in terms of the absolute units, that for 
capacity would read : 

A condenser is said to have unit capacity when one unit of elec- 
tricity will charge it to unit potential. Since by definition a con- 
denser has a capacity of one farad when one-tenth of the absolute unit 
of electricity charges it to a potential of 100,000,000, a farad must 

equal j^X loo-QOOOOO ""^^^ * absolute units of capacity. 

The definition of self-induction in term* of the absolute units 
would be: 

A circuit is said to have unit self-induction when, if the current in 
it is varied at the rate of one unit per second, the E. M. F. of self- 
induction is unity. Since by definition a circuit has a self-induction 
of one henry, when, if the current is varied at the rate of one-tenth of 
unit current per second, the E. M. F. of self rinduct ion is 100,000,000, 
such a circuit would have an E. M. F. of self-induction 10 times as 
great, or 1,000,000,000, if the current instead of being varied at the 
rate of one-tenth unit per second were varied at the rate of one unit 
per second. Therefore the unit of self-induction, the henry, is equal 
to 1,000,000,000 = 10» absolute units of self-induction. 

84. We can now add to our table of value in paragraph 82 the fol- 

A farad = y qqq qoo^ooO ^ ^^ ' absolute units of capacity. 

A microfarad = i Ano nnn ^ ^''*<1 = 10"*^ absolute units of capacity. 
A henry =1,000,000,000 = 10 ® absolute units of self-induction. 
A milliheuT}^ = . ^^.^ henry = 10® absolute units of self-induction. 


86. By agreement among electricians self-induction is represented 
by the letter L; capacity, by the letter C. 

Both self-induction and capacity are sometimes expressed in centi- 

Self-induction when expressed in t^rms of the fundamental units of 
length, mass, and time has the dimensions of a length, and the prac- 
tical unit of self-induction was formerly called a quadrant on account 
of the fact that in the metric system a meter represents, theoretically, 

10 000 000 P^^^ ^' ^^ earth quadrant — i. e., the distance from the 

equator to the North Pole. Since a quadrant = 1,000,900,000 centi- 
meters, and since the henry = 1,000,000,000 absolute units of self- 
inductance it may be said to = 1,000,000,000 centimeters. 

In this notation, which is still used by some \mters, a jnillihenr}" = 
1,000,000 centimeters. 

The units which have been considered in this chapter have been 
derived from the relations between electric currents and magnetic 
fields and are called electromagnetic units. Another system of units, 
also based on the centimeter, gram, and second, called electrostatic 
units, is in use. The relation between the absolute units of quantity 
in the two systems is the velocity of light in centimeters per second. 
This velocity is 30,000,000,000, or 3X10 ^° centimeters per second, 
and the electromagnetic unit of quantity =3 X 10 *® electrostatic units. 

The coulomb, being one-tenth of the absolute unit, =3X10" electro- 
static units. 

The electro-magnetic unit of potential is ^^^ of the electro-static 

In both systems a conderser is said to have unit capacity when 
unit quantity of electricity charges it to unit potential. 

From the definition of a/arad, given in paragraph 80, we see that the 
quantity of electricity in a condenser equals in coulombs the potential 

in volts multiplied by the capacity in farads, or Q = VC. '. C = ^^ and 
substituting for Q and V their unit values in electro-static units given 

Q y 10* 

above, C = — ^ — =9X10^S «r the practical electro-magnetic unit of 

capacity is 9 X 10*^ times as large as the electro-static unit. 

The capacity of spherical bodies is found to var>^ as their radii, and 
in the electro-static system a sphere of 1 centimeter radius has unit 
capacity; therefore the capacity of a sphere may be expressed by its 
radius in centimeters, and capacities are still expressed b}" some 
writers by the radius in centimeters of the equivalent sphere. 

A condenser having a capacity of 1 farad has a capacity equal to 
that of a sphere having a radius of 9 X 10*^ centimeters. 
2740—06 4 


A microfarad, = 10"* farads, is equal to a capacity 9 X 10** X 10"* = 
9 X 10^ or 900,000 centimeters. 

The earth's radius is approximately 65x10' centimeters; its 
capacity should be approximately 7,oOO microfarads. 

This difference in units is very confusing, but it exists, particularly 
with reference to the two qualities of self-induction and capacity, 
with which wireless telegraphy is intimately concerned. Microfarads 
and millihenrys, alone, will l)e used in tliis book, and where centi- 
meters are used, as they frequently are in catalogues of electrical appa- 
ratus and in books on electricity, the relations here given — 
1 millihenry = 1,000,000 centimeters, 
1 microfarad =900,000 centimeters, 
will enable one set of units to be converted into the other. 

The entirf system of units used in electrical measurements is a 
monument to the ingenuity of scientists, but productive of almost 
endless difficulties to students. 


86. We see that all conductors must have self-induction, because 
we know that all currents are surrounded by magnetic fields pro- 
duced by the currents. The production of the field creates an E.M. F. 
in fhe circuit opposite in direction to the E. M. F., causing the current 
and tending to stop it, so that self-induction has been defined in a 
qmiUtative manner as the inherent quality of electric currents which 
tends to impede the introduction, variation, or extinction of an electric 
current passing through an electric circuit. 

It has also been expressed in quantity as the number of lines of force 
induced in a circuit by the establishment of unit current in it. It , 
bears the same relation to electricity as inertia does to matter; it 
represents its resistance to change of condition, and it might be 
defined as the work necessary to create tmit current in a circuit. 

Suppose we wish to determine the work done in creating a current 
of value / in a circuit of self-induction L in a time T. 

Since L=the counter E. M. F. of self-induction when the current is 
varied at the rate of 1 ampere per second, the counter E. M. F. 

/ ' LI 

when it is varied at the rate of amperes per second = rp - If the rise 

in current is uniform, the counter E. M. F. is uniform and the total 
work done (which equals the product of the E. M. F., current, and 

time) would be equal to X /X T=L P were it not for the fact that 
the current rises uniformly from zero to / and its mean value is .^ and 
therefore the work done = ^^ . Since the factor of time does not 


appear in the result it shows that it requires the same amount of work 

to create a given current in a circuit of given self-induction whether 

it is created slowly or quickly and that this work is equal in joules to 

one-half the product of the self-induction in henrys by the square of 

the current in amperes. Therefore in a circuit whose self-induction is 

2 henrys the work done in creating a steady current of 10 amperes is 

equal to — ^ — = 100 joules = 73.7 foot-pounds. 

This 73.7 foot-pounds represents the energy stored in the magnetic 
field ; it is the work done by the circuit in creating its own field. If it 
is in the neighborhood of other circuits the momentary current cre- 
ated in them during the rise of current reacts on the field and makes 
the amount of work required still greater. 

When the current is broken the collapse of the field restores this 
energy to the circuit, thus tending to prolong the current. 

In alternating currents, where the rise and falLis continuous, the 
magnetic field is continually absorbing or giving out energy. In 
oscillating circuits the energy is constantly changing from magnetic 
to electric and vice versa. 


86a. Now suppose we wish to determine the work done in charging 
a condenser of capacity ^ to a voltage or potential Fin a time T, The 
potential of the condenser is zero before charging begins and increases 
as the charge increases, so that the resistance to charging also increases 
with the charge; therefore it must take more work to add a coulomb 
of electricity to a condenser of high than to one of lower potential. 

The total quantity of electricity in coulombs in the condenser is 
<2 = y C, and assuming that the condenser is charged at a uniform rate 

the coulombs per second flowing in to it = rp- and this must equal the 

amperes in the charging circuit. The condenser being charged at a 
uniform rate its potential will rise uniformly from zero to 1 ' and the 
total work done during the time T must equal the average potential 

V V vc y^c 

,y X rate of charge X by time =2 X y XT = *^. 

Since the factor of time disapj)ears, this shows that it requires the 

same amount of work to charge a given condenser to a given poten- 

' tial whether it is charged slowly or quickly, and that this work is equal 

in joules to one-half of the product of the capacity in farads by the 

square of the potential in volts. 

Therefore, in a circuit whose capacity is 2 farads, the work done in 

charging* it to a potential of 10 volts = — ^ =100 joules = 73.7 foot 

pounds. We see that it takes the same amount of work to charge a 


condensor whose capacity is 2 farads to a potential of 10 volts as it 
does to create a current of 10 amperes in a circuit whose self-induction 
is 2 hennas. 

If the capacity of the condenser is 2 microfarads instead of 2 farads 
the required work is one-milliontli of 73.7 foot-pounds = 0.0000737 foot 

Common potentials in wireless telegraphy are 30,000 volts and com- 
mon condenser capacities 0.014 microfarad. The work done in charg- 

14 (30,000)* 

mg such a condenser to 30,000 volts = . OOO 000 000 ^ ~ 2~ "" ^ 

14xi)00,000,000 ^ ., . , . , ...^ 

•> X 1 000 000 000 "" joules = approxmiately 4.6o foot-pounds. 

This 4.65 foot pounds represents the energy stored in the electric 
field of the condenser, just as the 73.7 foot-pounds referred to in para- 
graph So represented the energy stored hi the magnetic field. 



87. In an oscillating circuit, when the cimdenser is discharged — i. e., 
when the coatings are at zero potential — the electric energy has been 
transformed into magnetic energy. If tliere were no losses in the con- 
denser due to heating, etc., the conversion would be perfect, the work 
in the magnetic field of the circuit referred to in the preceding para- 
graph would equal 4.65 foot-pounds, and this, in turn, would be again 
transformed into electric energy when the c(mdenser recharges. (See 
par. 60.) 

A magnetic field can not be maintained steadily except by a current, 
but a condenser can be charged and kept in that condition for some 
time. However, condensers used in wireless telegraphy are always 
discharged immediately, and the energy stored in them before dis- 
charge is the stock in trade, so to speak, of the sending^ apparatus; it 
represents the work it can do on the ether. 

88. Let us consider a condenser having a capacity of 0.02 mf., 
charged to a potential of 30,000 volts. 

Such a condenser would contain ." - '^^ .w... =0.0006 coulomb, and 

would be capable of doing work equal to " ^ ~ -•== 9 joules = 

6.64 foot-pounds. 

If this condenser is discharged through a circuit having a self-induc- 
tion of such value (0.00125 millihenry) as will give a wave length of 
300 meters, the frequency of the circuit is 1 ,000,000, the alternations 
2,000,000 per second, and 0.0006 coulomb will create in such a circuit 
an average current of 2,000,000 X 0.0006 = / ^200 amperes. This shows 
the necessity for ample surface in condenser leads. 


If this energy is radiated in five complete oscillations, the rato of 
doing work, if the efficiency of conversion is "unity, is joules in 
T.irrf.inr^ second = 1,800,000 per second = 1,800 kilowatts. 

This shows that though the available energy is ver}" small the rate 
of doing work, that is, the power of a wireless telegraph sender, may 
be very great for an exceedfngly short period of time. 

The total work, 9 joules, looks much more formidable if read in ergSj 
since it equals 90,000,000 ergs. The only published experiments on 
the sensitiveness of wireless telegraph detectors (those of Professor 
Fessenden) state that in the most sensitive detector the least amount 
of work which will render a signal readable is 0.007 erg per dot, so that 
if we are able to concentrate approximately t¥:uoo:V«o (»o(f part of 
our energy on the receiving apparatus the signals sent out can be 



89. The fundamental electric equation /= p is derived from meas- 
urements of the relations existing between electric current and a con- 
stant E. M. F. in a circuit of constant resistance. 
• Self 'induction only affects a current when it is being started or 
stopped. It increases the time it takes for the current to rise to its 
steady value and the time it takes to fall to zero. For continually 
changing currents both in strength and direction it impedes both rise 
and fall, and therefore acts as a resistance, so that the resistance of a 
circuit for alternating currents is not the same as for steady or direct 
currents, but is a combination of the ohmic resistance and the induc- 
tive resistance or reactance (par. 29). Reactance is not a true ohmic 
resistance, which appears as heat, but is rather a counter or opposing 
E. M. F. 

The action is still further complicated in circuits having capacity, 
as wireless telegraph circuits have, since capacity is found to assist 
both the rise and fall of current and tlierefore to act in an opposite 
direction to the self-induction and to decrease the total resistance or 

In alternating circuits we have 7=^ where Z = the impedance = 

" 1 n^ 
27tNL— ^ — iV, being the frequency of the alternating 


Since capacity and inductance produce opposite effects, they can 

be used to neutralize each other, if 27tnL= ,y .^ the equation 

becomes /=p as for direct currents, E being the instantaneous 
value of the E. M. F. 

7/?' + [2 


In circuits where the resistance and capacity" are very small, as in 
primary sending circuits, / = approximately 27rnL, or the current 
depends almost entireh' on the reactance of self-induct'on. As will 
be seen later (from figs, referred to in par. 189), the current in 
wkeless-telegraph sending circuits is governed by reactance regula- 
tors placed in the primarj^ circuit. 


90. When the ratio of the resistance to the self-induction of a cir- 
cuit is small, and the circuit vibrates in its own period, the period is 
found to be equal in seconds to 27Cy/LC when L is measured in 
henries and C is measured in farads (see Appendix L.) This is 
called the fundamental equation of wireless telegraphy. 

If R is greater than 2y ^ the circuit will not vibrate at all. For 

instance, when a condenser is discharged through a wire of great 
resistance the charge leaks out slowly without any oscillation. 

A nonoscillatory condenser discharge, as compared with an oscil- 
latory discharge, is like the flow of molasses into a jar as compared 
with a large and sudden flow of water into a similar jar. One takes 
up a position of equilibrium slowly but surely, while the other 
vibrates and splashes and only settles down after a considerable 


91. We know that it takes time for electrical actions to take place 
and that one capacity or inductance may be equal in value to other 
capacities or inductances, but be made up differently with different 
materials whose resistance varies the .time it takes to create the 
electric or magnetic fields, respectivol3\ 

Every capacity and inductance has what is called its time constant. 
The time constant of a condenser is equal to C R — i. e., the prod- 
uct of its capacity and the resistance through which it is charged. 
If C is measured in microfarads, R must be measured in neghoms, 
and their product will then be in seconds. The greater the time 
constant of a condenser the longer time it will take for it to arrive 
at a given fraction of the charging potential. The amount which 
the potential falls short of its full value at any time T is a fraction 

of its full value equal to .y^-^^y t\' 

The time constant of an inductive circuit = p- The greater the 

time constant of a circuit the longer it takes to establish a current 
of giveu strength in it. The amount which the current falls short 


of its fiill value at any time T is a fraction of its full value equal 


92. Another eflFect of alternating currents on the apparent resist- 
ance of circuits is seen when the frequencies are above 100. It is 
called by Fleming the phenomenon of skin or surface resistance. 
The current seems to begin at the surface of a conductor and soak 
in, and to penetrate to the center it must have time. This is another 
instance of the time effect that must be kept in mind when dealing 
with alternating and oscillating currents. Lord Rayleigh has inves- 
tigated this effect and finds that for wires made of nonmagnetic 
material of diameter d the ratio between the resistance for frequen- 
cies of a million to the steady resistance is -« =-^--\/ -- n where 

p = the specific resistance of the wire. 

If the wire is of iron its resistance for high-frequency currents is 
still greater. 

The resistance of No. 16 wire for frequencies of. a million is 6.5 
times greater than its steady resistance. The larger the diameter of 
the wire the greater the proportional increase in resistance. Stranded 
wire, having proportionally greater surface than solid wire of the same 
area of cross section, offers less resistance to high-frequency currents. 

Flat ribbons, having larger surface, offer less resistance than cir- 
cular wire of the same area of cross section. 

' In the Stone receiving circuits, to be described later, the induc- 
tance coils are wound with wire of such size that for the frequency 
intended the current vnll penetrate to the center and there will be 
no waste material. Resistance is decreased bj" using a number of 
strands in parallel. 

Currents in wireless-telegraph circuits having a wave length of 
300 meters penetrate about ^\ millimeter, or approximately ^^^ 
inch inside the surface of the conductor. If the wires are of iron 
the current penetrates about wj/ou inch. 

We see, therefore, that oscillating currents used in wireless teleg- 
raphy, especially those in the closed circuit, not only maj^ be very 
large for a very short period of time, but that they remain practi- 
cally on the surface of the conductor, and it is evident that the latter 
should have much greater area than would be necessary to prevent 
heating by the same steady current. 



93. The capacity and self-induction of all but very simple forms 
of circuits is ver>^ difficult to calculate, and in general they are deter- 
mined b}" comparison with known values. 

The capacity of a straight, vertical wire of length I and diame- 
ter dj well above the earth and away from otlier conductors, is in 

micro-microfarads 0=^-^^^^-^ hg r2l\ 

Fleming states that a wire 111 feet long and diameter 0.085 inch, 
suspended vertically, was found to have a capacity of 0.000205 inf., or 
approximately one-tenth of one Slaby-Arco Leyden jar. Four wires 
of the above size and length, being 6 feet apart, were found to have a 
capacity of 0.000583 mf., or about three times as much as one wire. 

One hundred and sixty such wires in the shape of an inverted cone, 
2 feet apart at the top and in contact at the bottom, had a capacity of 
only about thirteen times that of a single wire. 

It will be seen that doubling the wire in an aerial does not double its 
capacity. For wires about 2 feet apart the capacity" increases approx- 
imately as the square root of the number of wires — that is, 16 wires 
would give four times the capacity of 1 wire. 

The self-induction of a straight wire of length I and diameter d ai.d 

circular cross section at a distance from other conductors is 2 Z (2.3026 

4 Z 
log. , — 1), values, being given in centimeters. The self-inductions 

of two parallel wires varies as the distance between them, decreasing 
with the distance, so that adding straight wire to an aerial does not 
add to its self-induction in the same proportion. 

The relation between the inductance and capacity of a straight wire 
of circular section and diameter small in comparison with its length is 
such that its electrical length is equal to its natural length, and its 
wave length is therefore twice its natural length. (See Appendix M 
for method of calculating inductances.) 


94. If a straight wire is broken in the middle the oscillation period 
of each lialf would be half the original period were it not for the fact 
that the adjacent ends of the wire and the air between them form a 
small condenser, which has the effect of slightly increasing the capacity 
of each wire, thus giving it a period slightly longer than half of the 
original period. 

If, the wires remaining as before, conducting plates are attached to 
adjacent «nds of each, this condenser is enlarged, its capacity increased, 
and the period of each wire lengthened, but the two wires or two open 


circuits, as we may call them, would vibrate in resonance and may be 
considered as forming one oscillating circuit of shorter period than the 
original wire. From the above it appears that we can shorten the elec- 
trical length of an aerial by putting a condenser in series with it, but 
we cannot shorten it to less than one-half its original period. 

.Vs we increase the size of the condenser the period increases, but it 
is found that a straight wire attached at one end to a large capa<5ity, 
such as the earth, has a wave length (like that of an organ pipe open at 
one end and closed at the other) equal to four times its natural wave 
length, so that by increasing the capacity sufficiently the wave length 
could be doubled. 

We know, however, that by coiling the wire we can increase its wave 
length to any amount we desire, so that capacity is only added in 
series for shortening the wave length of aerials; they are lengthened 
by adding inductance. (See fig. 40a, illustrating Telefunken receiv- 
ing sets.) • 


94a. Ix>oking at this from another point of view we find that two 
equal condensere in series have only half the capacity of one, while two 
equal condensers in parallel have twice the capacity of one. Con- 
densers follow in this respect the law of resistance. Conductivity is 
the reciprocal of resistance, and the total conductivity of two resist- 
ances in parallel is ^qual to the sum of their separate conductivities. 

This fact has a practical use in wireless-telegraph condensers where 
any particular voltage is used. Condensers which will be ruptured if 
used alone can be used in series, dividing the voltage between them. 

For instance, take a transformer giving 30,000 volts to be used in 
connection with condensers that will stand but 20,000, by placing 2 
in series each condenser would have to stand but 15,000 volts. 

It will be seen that 32 jars made up into 2 condensers of 16 jars, in 
parallel, in each and the two condensers placed in series would only 
have the capacity of a single condenser of 8 jars in parallel, but the 
work on each jar would be four times lighter. 

Chapter III. 



96. We are now in position to speak in more specific terms of the 
work done in sending wireless telegrams. 

Let us suppose that we are delivering 2 kilowatts at 60 cycles and 
110 volts to a transformer, which delivers it to a condenser at a maxi- 
mum potential of 30,000 volts. 

Two kilowatts = 2,000 watts = 2,000 joules per second = 1,474 foot- 
pounds per second. 

Since 60 cycles = 120 alternations per second, the work equals 
approximately 12.3 foot-pounds per alternation. 

If the work done on the condenser is in phase with the charging 
E. M. F., and if the spark gap is set to hreak do>Mi at a potential of 
30,000 volts, the condenser will be discharged at the peak of the charg- 
ing curve or when one-half of the work that can be done in an alterna- 
tion (6.15 foot-pounds) has been done on the condenser. The capacity 
of a condenser which takes 6.15 pounds of work to charge it to 30,000 
volts = 0.0186 mf., or approximately nine 0.002 mf. jars in parallel. 

96. Suppose we are sending at the rate of 20 words per minute, that 
the words average 5 letters each, and that each letter is made up of 3 
characters equal in length to 9 dots, then a minute can be repre- 
sented as equal to 20X5X9= 900 dots = 1 5 dots per second."^ In other 
words, the length of a dot is one-fifteenth of a second. Now we have 
120 alternations per second, so that we have about 8 alternations per 
dot when sending at the rate of 20 words per minute; therefore a dot 
is made up of 8 distinct sets of discharges of the condenser and a dash 
of twice or three times that number. The condenser is doing work 
in producing ether waves at the rate of 6.15 foot-pounds per alterna- 
tion equaling, approximately, 50 foot-pounds per dot and 100 foot- 
pounds per dash. 

97. It will be noted from the text that at this sending rate the fi*e- 
quency necessary to give 1 alternation per dot and 2 alternations 
per dash is only 7i cycles per second. 

It will be noted further that we can not utilize 2 kilowatts continu- 
ously. We can only use it in charging the condenser during the first 
half of each alternation. As soon as the discharge begins the con- 




denser circuit oscillates in its own period as if entirely disconnected 
from the transformer. 

In this respect the charge and discharge of a condenser resembles 
the loading and firing of a gun. We must bear in mind, however, that 
though the charging may be done at any rate we desire, the discharge 
is very much more sudden than that of any gun. 

It is not necessary, therefore, except when considering methods of 
regulation, to devote attention to the charging of the condenser, and 
our minds can be concentrated on what happens during its discharge j 
when it forms part of an oscillating circuit. 

98. It was stated in paragraph 62 that the period of electrical 
vibration of any circuit depends only on the capacity and self-induc- 
tion of the circuit, and in paragraph 90 that, when the ohmic resist- 
ance of the circuit is small, the period (the time of one complete 
vibration) is equal to 2ny/i^(J^ where L is the self-induction in 
henrys, C the capacity in farads, and n the ratio of the circum- 
ference of a circle to its diameter. 

This shows that a circuit having a self-induction of 1 henry and a 
capacity of 1 farad would have a period of 2;r =6.2832 second. Its 
electrical length would be equal to approximately 584,000 miles and 
its wave length would be 1,168,000 miles. 

The standard wave length originally adopted for naval wireless 
telegraph stations was 320 meters; the electrical length of such cir- 
cuits is 160 meters, and their period approximately ^o o^oou second. 
That is, they make approximately 900,000 complete vibrations per 
second. The usual capacity in these circuits was 0.014 microfarad 
(seven 0.002 mf. jars in parallel). Therefore the self-induction must 
have been 0.0022 millihenry. 

It will be noted that the period of a circuit varies as the square root 
of the product of the inductance and capacity, so that doubling either 
of these increases the period by %/2, i. e., to 1,432 times its former hff/' 
value. Doubling both inductance and capacity doubles the period. 

99. By comparison with standard inductances, and capacities, the 
capacity and self-induction of circuits can be measured and their 
periods calculated. Their periods can also be directly measured by 
measuring the time between successive sparks. This is done by 
l)hotographing the sparks by reflection from the surface of a rapidly 
revolving mirror. The movement of the mirror between sparks sepa- 
rates their images on the photographic film, and knowing the num- 
ber of revolutions of the mirror per second, the ela])sed time between 
sparks can be calculated. 

Prof. G. W. Pierce, of Harvard University, has measured the 
period of some t\^pes of oscillating circuits used in wireless teleg- 
raphy, and it is from his published account of his experiments that 
the following description is derived. 


Suppose a sj)ark gap set to break down at a potential of 10,00() 
volts, to be used in a circuit where the maximum potential reached 
in the condenser is 30,000 volts. 

Let the curve of sines in fig. 18 represent the condenser potentials 
of the oscillating circuit during 2 alternations, each lasting ^i^ of a 

The resistance of the spark gap is practically infinite before the 
potential reaches 10,000 vohs, and therefore no current passes. 
When the potential has risen to 10,000 volts the spark gap is ruptured. 
Its resistance decreases instantly to a fraction of an ohm, and during 
the first half of the oscillation the condenser is discharged to zero 
potential. During the last half of the oscillation it is chained again 
m the opposite sense. The sparks pass first in one direction and 
then in the other, and the spark gap not regaining its resisting quali- 
ties, the oscillations or surgings continue until the potential (owing 
to losses due to the radiation of energy in the shape of electric waves 
to heating the circuit, and the light and heat at the spark gap) does 
not rise high enough to disnipt the gap. 

The transformer immediately recharges the condenser, which as 
soon as it again reaches a potential of 10,000 volts breaks do\VTi the 
spark gap again, and a second series of oscillations begins. 

In the circuit under consideration the maximum charging poten- 
tial is 30,000 volts, so that a condenser wdth a spark gap breaking 
down at 10,000 volts may be charged and discharged several times 
during one-half cycle of the charging current. 

Fig. 18c is an attempt to show graphically the oscillating discharge 
of a condenser, when the spark ga]) is set to break do^^^l at the maxi- 
mum charging potential. (Fig. 18c cannot be drawn to scale on 
account of the very short lengtli of time it takes to discharge the 
condenser, compared to the time it takes to charge it.) 

The spark acts like a trigger which suddenly releases the stored 
energy in the condenser, and as soon as this energy has been radiated, 
the trigger autcunatically resets its(*lf and does not release again 
until the condenser is recharged. 

100. The electric waves produced during one set of oscillations 
are called a ivave train. The wave trains produced during one-half 
cycle of the charging current are called a group of wave trains. 

The duration of a wave train is the time of one oscillation multi- 
])lied by the number of oscillations in the train. 

It is found that the duration of a wave train is much less wlien the 
oscillating circuit is connected to an auto transformer, as in fig. 14d, 
or to an ordinaiy air core transformer, as in fig. 29, with one end free 
and the other earthed, like C D in fig. 29, than when it oscillates 
without any other electrical connection. The energ}^ is radiated 
more rapidly, the vibrations more quickly damped. For tliis reason 


the circuit formed by the condenser, spark gap, and inductance is 
called the closed or oscillating circuit; that fonned by the aerial, 
inductance and ground connection, the open or radiating circuit, 
(See par. 70.) 


101. When the closed and open circuits have some turns of induc- 
tance in common, as in fig. 32, they are said to be direct connected; 
when they have no common turns, as in fig. 29, they are'said to be 
inductively connected, *' ' 

It is found that when the common turns in direct connected circuits 
are large in number, or the coils of inductively connected circuits 
close together, the damping is greater, and the energy being there- 
fore radiated faster, the duration of a wave train is less. Such circuits 
are said to have close or tight coupling, and they are found to have 
two periods of vibration — one longer and the other shorter than the 
natural electrical period of either circuit. 

When the coils of inductively connected circuits are not very close 
together, or the common turns in direct connected circuits are com- 
paratively few, the transfer of energy from one circuit to the other is 
slower, the damping less, and the duration of a wave train greater. 
Such circuits are said to have loose coupling, and it is found that the 
looser the coupling the more nearly the two periods of vibration of the 
coupled circuits approaches the natural period of each. 


102. We see, therefore, that the duration of a wave train depends 
on the coupling or the mutual induction between the oscillating and 
radiating circuits. It also depends on the self-induction in each cir- 
cuit. The interval between wave trains depends, however, on the 
pow-er supplied to the transformer (the foot-pounds of work it can do 
in a given time) for charging the condenser and on the tijne constant 
(see par. 91) of the latter and on the length of the spark gap. If the 
condenser has a capacity of 0.02 nif., the work necessary to charge it 
to 10,000 volts = 1 joule, or 0.737 foot-pounds, so that it will require 
about f ffVir second for a power of 2 Icilowatts to charge it to that 
potential. If the current has a frequency of 900,000 and there are 
nine complete oscillations in one wave traini the duration of a wave 
train is jj^^^^ second, so that the time necessary to charge the con- 
denser may be fifty times as long as the time taken to discharge it. 

In such a circuit, if we do work at the rate of 2 kilowatts in charg- 
ing, we do it at the rate of 100 kilowatts in discharging. 

If the waves are so rapidly damped that the condenser is discharged 
in one complete oscillation, the whole energy" will be radiated in 
««ijWiy second, or at the rate of 900 kilowatts. 


The effect of quickly and slowly damped wave trains on detectors 
will be discussed later. 

It is evident that if the spark gap in the circuit under consideration 
is adjusted to 30,000 volts but one discharge of the condenser per 
alternation will take place and but one train of waves will be ser.t 
out. Shortening the gap will increase the number of discharges per 

The exact number for any spark-gap length will depend on the time 
of an alternation — i. e., the frequency, and on the length of time it 
takes the available power to charge the condenser to the voltage 
required to break down the gap. Less energy per wave train will be 
radiated on a short gap than on a long one, because the work done 
varies as the square of the voltage (see par. 86) ; but the total work 
done may be equal, on account of the greater number of dischar«:es. 

N. B. — It is on this account that a hot-wire ammeter (see par. 180) 
is not always a good indicator of the best adjustment of a wireless- 
telegraph sending circuit. Its readings indicate the total energy radi- 
ated instead of the energy in any particular wave train. If, however, 
the amplitude of the waves in each train is not great enough to pro- 
duce readable effects in the detector, the group of wave trains in a 
single alternation will not help matters, because the wave trains are 
so widely separated in comparison with their length that the effect of 
one train on the detector has disappeared before the succeeding train 

103, If the spark gap is too short, an arc is formed and no oscilla- 
tions take place except those due to the frequency of the charging 

104. Professor Pierce has sho\vn that the interval between wave 
trains may vary on account of the residual charge left in the con- 
denser. When the spark gap's original resistance is restored, the 
potential of the residual charge may be opposed to the potential of 
the transformer and delay the charging. He has shown also that the 
gap sometimes partly retains its conducting character and breaks 
dowii at a lower potential than its length would indicate. This makes 
the sparks and osciUatioiis irregular in strength and number and pro- 
duces ragged and poor signals. 


106. The dielectric strength of air is considered to be about 4,500 
volts per millimeter for gaps of about 1 millimeter in length, and about 
3,000 volts per millimeter for gaps of the length of a centimeter or 
more. Fig. 30 shows sparking distances in air between needle points, as 
determined by experiment. These distances are usually greater than 
those produced by equal voltages between the blunt spark points used 
in wireless telegraphy. The latter probably correspond more closeh 


to the table given in Appendix A. On the other hand, the table of 
spark distances is determined by raising the voltage verj^ gradually 
and exactly alike for each gap, while in oscillating circuits there is a 
convulsive rush which may produce very high potentials. This has 
been shown by introducing a minute spark gap elsewhere in the cir- 
cuit, the effect being to greatly increase the gap, which can be rup- 
tured by a given transformer potential. The inertia of the charge 
carries it forward, and just as the inertia of water in a pipe produces 
a great pressure if its flow is suddenly checked, so the potentials in 
the sending circuits may, and usually do, rise much higher than is 
indicated by the transformer ratio. 

106. From the foregoing discussion we see that the real source of 
power in wireless telegraphy is the condenser, and that we can only 
use it intermittently, not more than one-fiftieth of the time, in fact, 
but that while working it works very energetically. 


107. A certain amount of inductance is necessary in the closed cir- 
cuit in order to transfer energy to the open circuit, whether the 
circuits are direct or inductively coupled, and since condensers of 
any desired capacity can readily be obtained, it is easy to make 
the closed circuit any electrical length we desire. 

The open circuit, while it has concentrated indactance like the 
cl6sed circuit, has distributed capacity which is comparatively small, 
and though any electrical length we desire can be obtained by adding 
inductance, it is found that concentrated inductance beyimd that 
necessary to receive energy from the closed circuit lessens the radia- 
tion, and on that account it is necessar^'^ to increase the period of 
the open circuit by adding wires to the aerial. We have seen that, 
unless they are quite a distance apart, two parallel wires do not 
have twice the capacity of one, so that it is practically difficult to 
fret very long wave lengths in the open circuit, especially on ship- 

The wave lengths that we can efficiently use in the open circuit 
are therefore limited by practical considerations. 

Since the energy in any discharge varies as the square of the 
voltage, and since any desired voltage can readily be obtained, the 
work that can be stored in a condenser of given capacity depends 
only on the dielectric strength of the condenser material. We find, 
however, that very high voltages, on account of difficulty of insu- 
lation, break out in sparks at all points of the circuit, tliat the 
aerial wdre glows throughout its length, and the whole apparatus 
generally acts like a dry linen fire hose when subjected to a high 
water pressure — i. e., it spurts electricity at all points in all directions. 


So practical considerations limit the wave lengths that can be " 
efficiently used on board ship, and also limit the power that can be 
used with them. 



108. It is probable, though this has not been definitely proved, 
that the best results with any given sender are obtained when the 
work necessary to charge the condenser to the transformer voltage 
is equal to that supplied by the available power of one-half alter- 
nation. (See par. 95.) This gives but one wave train per alterna- 
tion, and, if true, fixes at once the capacity of the closed sending 
circuits for any given power. Good results, however, have been 
obtained by using a shorter gap, and thus more than one wave train 
per alternation, and also by producing a condition of resonance in 
the secondary circuit with the primary frequency and obtainin^r a 
wave train only every two or more alternations. 

By the first method waves of the greatest amplitude (and there- 
fore containing the greatest amount of energy) of which the set as 
a whole is capable are sent out every alternation, and, other things 
being equal, they should be detected at the greatest distance. 

By the resonance method such waves are sent out every second, 
third, or fourth alternation. (See par. 147 and footnote.) 

109. Having seen that large currents flow during the oscillating 
discharge of even a comparatively small condenser, and that owing 
to the high frequency these currents are only on the surface of the 
conductors, the necessity for ample surface on condenser connections 
and inductances is obvious. 

110. A large number of the sending circuits in use at present are 
of the direct connected type, like the auto-transformer shown in 
fig. 82. 

The ^^'ave length of the open and closed circuits is made variable 
at will, and change of coupling without changing the wave length 
of either circuit is made possible by the use of three variable con- 
nections, as shown in fig. .32. It will be seen that the closed cir- 
cuit has one permanent and one variable connection to the sending 
inductance, or helix, and that both the aerial and ground connec- 
tions are variable. Condensers in sending circuits are not usually 
variable, though they are frequently in parallel, as in fig. 31, or in 

Footnote, — With a given transformer and given condenser capacity the power that can 
be obtained in any wave train depends, when using the resonance method, on the d<impinij 
in the secondary circuit (condenser and transformer-secondary) as well as the power iu 
the primary circuit. Tliis fact modifies the statejnents in par. 108 and shows that the 
power of a sending set may not depend entirely on the size of the motor-generator used 
with it. 


series, fig. 31s. Condensers in series may be on either side of the 
spark gap, as in fig. 31b. 

Series-parallel connections are also used, just as in primary 

It mil also be seen that instead of connecting the spark gap 
across the power leads from transformer to condenser, that the con- 
denser may be placed across these leads and the spark gap in one 
leg or the other, as in figs. 33 and 34. 


111. Fig. 32 shows the connections of the Slaby-Arco sets — i. e., 
spark gap across secondary leads, condenser in one leg of secondary' 
lead and made up of seven Leyden jars in parallel, each jar of 0.002 
mf . capacity. 


112. Fig. 33 shows the connections used in the Massie sets. The 
spark gap and condenser are interchanged, as compared with the 
Slaby-Arco. In the Slaby-Arco sets the condenser is charged on 
one side directly from the transformer and on the other through 
the inductance, but the self-induction of the latter is so small that 
its time constant must be small and the charging of the condenser 
very little, if at all, delayed. 

The Massie condensers are made up of glass plates covel'ed with 
tin foil; capacity of each plate, 0.0083 mf. Plates can be connected 
in groups and used in parallel, series, or series-parallel, as desired. 
The glass is used as the dielectric, though this type of condenser can 
be connected so as to use the air between the plates as the dielectric 
if desired. 


113. Fig. 35 shows the connections of the Fessenden sets. If this 
figure is compared with that showing the Slaby-Arco connections, it 
will be seen that the condenser has been moved to the other leg of the 
secondary leads, and that the ground lead instead of being direct 
from the inductance, as in the Slaby-Arco (and other sets to be 
d^cribed), is taken off between the condenser and the transformer. 
This gives the aerial a path to ground through the condenser or spark 
gap. All other sets have direct path from aerial to ground, and path 
through condenser and spark gap. 

One leg of the secondary, being directly grounded, if the aerial be 
touched while curfent is on the transformer the circuit is completed 
and a severe shock may be felt. This method of connection must also 
be taken into consideration while adjusting the closed and open cir- 
cuits to the same natural wave length. 

2740—06 o 


The Fessenden 2 kilowatt ship sets are furnished with condensers 
of 0.004 mf . capacity, made up of tin-foil-covered glass or niica plates 
in paraffin, or with tin-foil-covered plates either in compressed air or 
air at ordinary pressure, the paraffin in the one case and the air in 
the other being used as the dielectric. 

This capacity is less than one-third of that used in the Siaby-Arco 
sets, but the method of connection — i. e., grounding the circuits between 
the condenser and transformer — tends to increase the apparent 
capacity by keeping the earth and the aerial oppositely charged. 
With this low capacity the inductance of the sending circuit must be 
made correspondingly large in order to retain the same wave length. 


114. Fig. 34 shows the connection of the De Forest and Shoemaker 

It will be noted that the only change from the Massie sets is that 
the spark gap is changed to the other leg of the secondary, which 
brings one side of the gap in direct connection with the ground. 

The De Forest sets for ship use have Leyden jar condensers of 
5 to 9 jars capacity .002322 mf. per jar. For large sets the De Forest 
Company uses tin-foil-covered glass plates in oil. 

The Shoemaker sets are furnished either with regular Leyden jars 
or with tubes. (Leyden jars open at both ends to give circulation of 
air.) The total capacity varying with the power desired. 


116. The Telefunken Company uses the same connections as the 
Slaby-Arco and furnishes Leyden jar condensers of various types and 


116. Fig. 36 shows the connections of the Stone sets, which are induc- 
tively connected, as distinguished from the direct-connected sets 
which have been under discussion. Tliis inductive connection is 
shown diagrammatically in fig. 36. As actually constructed, the closed 
circuit is the same as in any other set, and has one variable connection 
to the inductance; but the open circuit inductance is mounted above 
that of the closed circuit, as shown in fig. 36a, and has one variable 

The entire aerial helix is also movable at will, so that the mutual 
induction between the two circuits, and therefore the coupling, can be 
varied at will. 

The Stone Conipanj^'s condensers are made of tin-foil-covered glass 
plates embedded in a mixture of beeswax and rosin, or the glass may 


be dispensed with and the beeswax and rosin mixture with intervening 
sheets of tin foil alone used; ordinary sets are made up of seven con- 
densers in parallel, each of 0.0015 mf. capacity. 

Condensers are made up in rectangular blocks of six or more plates 
each and stowed on shelves in a wooden condenser case. These blocks 
can be connected in parallel or in series, or in a combination of the two, 
as desired, depending on the voltage and capacity. 

117. Efficiencies of diflFerent types of senders (see present par. 126). 


118. Practically nearly all insulators have a greater specific induc- 
tive capacity than air at ordinary pressure, and nearly all of them 
have a greater dielectric strength than air. The Leyden jar, having 
long been used as a high-potential condenser, its method of manufac- 
ture being well known, and the best glass having not less than nine 
times the capacity of air, has been very generally used in wireless-tele- 
graph sending circuits. Air and oil, while requiring much larger vol- 
ume to give the same capacity as glass, have the excellent property of 
mending themselves after puncture by a spark, while all kinds of solid 
or semisolid dielectrics require renewal after rupture. 

Mica has very great dielectric strength, as much as ofiOO volts per 
mil and has been used to some extent in condensers in the form of 

The semisolid dielectrics, such as beeswax and paraffin, have to 
be made up with considerable attention to the temperatures in which 
they are to be used, since they may melt in summer and crack in win- 
ter, but are cheap and easily obtained. Another quality of dielectrics 
which governs their use to a certain extent is what is known as their 
h3''steresis loss. 

When a piece of iron is magnetized and demagnetized — i. e., goes 
through a cycle of magnetization — a certain amount of energy is 
expended, which appears in the shape of heat in the iron. It is sup- 
posed to be due to internal friction in the molecules of the iron and is 
•called magnetic hysteresis. 

In the same way, to put a condenser through a cycle of charge and dis- 
charge requires the expenditure of a certain amount of energy, which 
appears as heat in the dielectric and is called dielectric hysteresis. 
The loss of energy due to this quality varies in different dielectrics and 
is a function of the frequency. . Loss of energy due to sparking from 
the edges of the tin foil around the edges of the dielectric to the oppo- 
site foil is frequently noticed. This can be partly remedied by cover- 
ing edges of foil and plates with an insulating compound. Fleming 
has shown that the lengths of discharge paths of all condenser elements 
should be equal. 


119. Tables showing the specific inductive capacity of a number of 
different dielectrics and their dielectric strength are given below. 
This data is incomplete. Data relative to the hysteresis losses of 
various dielectrics is almost lacking, and want of agreement is noted 
among different authorities. 

Material ' 'l^^^ 

ive ca- 


Air 1 



I a 4, TRW 

* 3. Olio 

Hard rubljcr 2. 29 * 40, 000 

India rubber 2. 10 e 30, 000 

Mica 6. W e eo, 000 

Micanite e 40,000 

Typewriter linen paper f 45, OCO 

Parafline oil 2.71 

Qlaas (crown) 6.96 

Glass (plate) 8.45 

Glass (light flint) 6. ?2 

Glass (extra dense flint) 9. 86 I 

a Per millimeter for thicknesses up to 1 millimeter. « Per millimeter. 

f> Per centimeter. <* Approximate. 

Dielectric strength per millimeter increases with decrease of thick- 
ness, except in oils where it seems to decrease. 

Dielectric strength of air increases with increase of pressure. 

Dielectric strength of air decreases with decrease of pressure until 
the pressure is in the neighborhood of 1 mm. of mercury, when it 

Dielectric strength of a vacuum should be infinitely great. 

Mica if it could be obtained in large sheets would be the best mate- 
rial for the dielectric of condensers for use in wireless telegraphy, hav- 
ing both high specific inductive capacity and great dielectric strength. 

120. Fleming states that with the best flint glass it is possible to 
store about 45 foot-pounds of energy per cubic foot of glass. The 
limit is set by the dielectric strength of glass. Capacity varies inversely, 
as the thickness and dielectric strength, directly y as the thickness of the 
dielectric, but they do not vary in the same ratio. 

The dielectric strength of glass condensers decreases, that of oil con- 
densers increases, with the frequency. 

An indestructible form of condenser can be made up of metal plates 
in compressed air. The metal plates being already conducting do not 
require tin-foil coverings. Compressing the air gives it great dielec- 
tric strength, and should this be exceeded the air at once repairs the 

An entirely satisfactory form of condenser for wireless telegraphy 
has not yet been designed. 



121. The sending key in small sets is placed in one leg of the pri- 
mary' circuit between the source of current and the transformer or 
induction coD. 

PI. XXII shows the Morse key furnished with Slaby-Arco sets. 
It is of massive construction, with heavy platinum-tipped contacts. 
Several types are furnished, one with a magnetic blow-out for extin- 
guishing sparks ; another with a hinged contact plate having the arma- 
ture of an electro-magnet attached to it. The primary current ener- 
gizes the electro-magnet, which holds its armature when down till the 
current is interrupted, when it is drawn up by its spring, and the key 
contacts separate without spark. 

Condensers are shunted around sending keys in some cases to 
absorb the induced current wliich causes the spark at break. Most of 
the other sets furnished use the ordinary telegraph key, with some- 
what larger contacts. Silver contacts of comparatively large diam- 
eter are used with the Stone keys. In all keys the contacts must be 
kept smooth and their faces parallel. 

For breaking large currents various devices are employed, that 
most generally used being to energize a solenoid by closing the sending 
key, the solenoid armature making and breaking the primary current 
in oil. 

Sending keys are shown in outline in figs. 65 to 71, inclusive. 

The method of installing the key in shunt with an inductive resist- 
ance and in series with another inductive resistance is shown in fig. 70 
and in standard diagrams, figs. 72, etc. 

For sending time signals a Western Union relay is used to close a 
local battery, which energizes an electro-magnet whose armature car- 
ries a lever which presses and releases the sending key in imison with 
the impulses sent from the standard clock at the Naval Observatory. 
Sending keys should have just sufficient movement to prevent arcing 
and permit well-defined movement in making and breaking. 


122. The table of sparking potentials given in Appendix A and 
referred to in paragraph 105 and the curves showing sparking poten- 
tials between needle points are obtained from constant potentials. 
While the first spark in each wave train in wireless telegraph sets 
depends on the transformer potential, succeeding sparks depend on 
the shape and constants of the oscillating circuit and the material of 
the spark points. 

The spark must be kept white and crackling — if too long, it will be 
stringy; if too short an arc will be formed. 

There is no doubt that much of the irregularitv noticed in sending is 
due to irregular action in the spark gap. 


Professor Pierce notes an increase of received energy of 400 per cent 
when using a Cooper-Hewitt mercury interrupter in place of an ordi- 
nary spark gap, which indicates the great amount of enei^ that must 
be lost in the gap. The mercury interrupter, however, is diflScult to 
keep in good adjustment. 

A great deal of thought and ingenuity has been expended in the 
direction of improving the action of spark gaps. For instance, the use 
of magnetic blow-outs, induced and forced air drafts across the gap, 
dividing it into a series of short gaps, placing gaps in parallel, enclosing 
them in compressed air and in nitrogen gas, cooling hollow spark 
points with air and water. None of these are markedly better, except 
when large powers are used, than the ordinary gap in air between two 
zinc rods about one-fourth of an inch in diameter. There are two 
points common to all spark gaps which are necessary for good work- 
ing (a) the points or balls must be smooth and clean; (b) they must be 
kept from heating. 

The effect known as " soaring '' is probably due to inequalities in the 
action of the spark gap and condensers. * 

' Zinc is the best of all metals for spark-gap electrodes. • Its action 
in relation to electric discharges is almost as peculiar as that of iron in 
relation to magnetic effects. 

Brass is probably the next best. 

All spark gaps should be well muffled, for obvious reasons. 

Slaby-Arco sets are fitted with plain zinc spark electrodes. 

Telefunken sets are fitted with a number of gaps in series, any num- 
ber of which can be included at will. 

Stone ship sets are fitted with six gaps in parallel, between brass 
spark balls. 

Fessenden and De Forest ship sets have the gap divided into two 
parts by a movable disk, whose center is out of the line joining the 
spark electrodes, so that the points of the disks through which the 
spark passes can be varied at will. All spark gaps are adjustable. 
Provision is made for cooling them except in case of small sets. 

In the large Massie sets the electrodes are kept cool by being made 
hollow, with fine holes, through which compressed air is forced, drilled 
from the outside to the hollow center. 

The increased radiation with the cooled spark points is very evident. 


123. Let fig. 50 represent a closed circuit inductively connected to 
an open circuit with a vertical air wire, and suppose the spark gap to 
break down at the point of maximum potential of the charging cur- 
rent. At this instant there is no current flowing in the closed circuit, 
and therefore no current and no charge in the open circuit; the energy 
is all electrostatic, all in the closed circuit, and practically all in the 


electrostatic field between the condenser plates, the capacity of the 
spark points and other parts of the circuit being very small. 

As soon as discharge through the spark gap commences, the field of 
the current in the closed-circuit inductance induces movements of 
electric charges in the open circuit, positive in one direction, negative 
in the other, the starting point of the disturbance being the open-cir- 
cuit inductance. As the charges separate they are connected by elec- 
trostatic lines of force and surrounded by magnetic lines of force, both 
moving outward at the same rate that the charges move in a straight 
wire, so that the whole action appears like that of a rapidly growing 
sphere, having the wire for an axis. The magnetic field around the 
wire becomes a maximum at the end of a quarter period, but the elec- 
trostatic field becomes a maximum at the end of a half period, at 
which time the magnetic field has partly collapsed on the wire and the 
charge at the top of the aerial reaches its maximum potential. The 
spherical condition has been maintained only imtil the charge repelled 
to ground reaches the ground, when it travels off, guided by the groimd 
plate and the moist earth connected therewith, so that, at the expira- 
tion of a half period of the closed circuit, conditions in the open cir- 
cuit are eLa^sitoWn. in fig. 50a, with the energy all electrostatic in both 
circuits. ' 

Duriaa^^he fii^t half of the second half period the energy in both cir- 
cuits unites in creating an electro-magnetic field in the opposite direc- 
tion iff fbc aerial, while the electrostatic field tends to collapse on the 
wire. ^ 

During the second half of the second half period the reversed elec- 
tro-magnetic field tends to collapse on the wire, while an electrostatic 
field, reversed in direction, is created, reaching a maximum at the end 
of the period. li^- 

If the charges can be represented as meeting in the open-circuit 
inductance, the electrostatic field at the middle of the second half 
period can be shown as in fig. 50b, where the mutual repulsion of the 
lines of electrostatic force outside of the wire have kept them from 
returning as fast as the charges travel up and down the wire. As 
these charges pass each other the ends of the lines unite and become 
closed circuits (fig. 50c) or electric whorls shaped like smoke rings, 
which, owing to their mutual repulsion, expand in all directions except 
toward the air wire, because their direction on the side next the air wire 
is coincident in direction with that of the outside of the succeeding 
whorl, and therefore the two are mutually repulsive and do not neu- 
tralize each other. i: 

124. It is in this manner that we cd^ceive energy to be detached and 
sent off into space from wires formisig open oscillating circuits. The 
expanding rings soon touch the eartn and are guided by it, as by any 
other conductor, thus resembling at a short distance from the wire 


expanding hemispheres. In these hemispheres the magnetic lines of 
force are the parallels of latitude, the electrostatic lines are the merid- 
ians. The maximum strengths of field due to each, are a quarter of a 
period apart. Each one is zero where the other is a maximum. 

Considered from tliis point of view the energy in any part of the field 
should vary as the square of the distance from the radiating wire. 

126. The direction of the magnetic lines of force at any point is par- 
allel to the earth's surface and at right angles to a line joining the 
point with the source of radiation. 

The direction of the electrostatic lines of force at any point is per- 
pendicular to the earth's surface. 

The earth's magnetic lines of force, whose direction determines the 
direction in which magnets point, are parallel to the magnetic lines in 
electric waves at points east and west of the radiating wire and at rio^ht 
angles to them at* points north and south of the radiating wire. In 
east and west directions the magnetic waves alternately reenforce and 
oppose the earth's magnetic force. In other directions their eflFect 
varies with the direction. An iron wire placed horizontally at ri^ht 
angles to the line joinmg its position with the radiating station would 
be parallel to the lines of magnetic force and woidd become magnet- 
ized, just as iron wires held in the magnetic meridian become magnet- 
ized. Pointed in the direction of the station this effect would be zero. 
It has been proposed to utilize this fact, both as a detector of electric 
waves and of their direction. 

Any conducting wire held perpendicular to the earth will be cut 
at right angles by the magnetic lines of force, and will have electric 
charges induced in it which will create currents, and it is by means 
of the currents thus induced in vertical conductors that electric 
waves are usually detected. 

It also has a difference of potential, created in its ends by joining 
two points of the advancing wave whose electric potential diflFers. 

If two horizontal conducting plates, forming a condenser, are in 
the path of the wave, they will have electrostatic charges of dijffer- 
ent potentials induced on them, and if joined by a conductor, oscil- 
lating currents will be produced in the conductor. 

We see, therefore, that there should be at least four ways of detecting 
electric waves, viz: (a) By placing conductors at right angles to the 
magnetic field; (h) magnetizable bodies parallel to it; (c) by plac- 
ing conductors parallel to the electric field; (d) conducting planes 
forming condensers at right angles to it. 

It would seem that by the last method we should be able to abstract 
the greatest amount of energy from the wave. 

126. It will readily be seen that the induction of currents in 
another aerial, however great the distance from the inducing wave, 
is not different in principle from the inductive actions of the wires 


A B and C D on each other, which has been discussed in the early 
part of this book. 

It was there pointed out that the inductive actions caused by ether 
movements could have no limits, however small they might be at 
great distances. In other words, every change of current sends out 
some nonretumable energy. Oscillating circuits of high frequency 
appear to send out more nonretumable energy than those of the low 
frequencies used for lighting and power. 


Sheet 31 — 117. The efficiencies of the various forms of closed cir- 
cuits shown in figs. 32, 33, and 34 diflFer, if at all, only on account of 
the materials of which they are made and their dimensions, since 
they are the same in principle. 

The means of connecting them to the open circuit are also prac- 
tically alike. 

Whether direct or inductively connected sets are the more effi- 
cient has not yet been definitely determined. Inductive coupling 
offers a convenient means of weakening the mutual induction, and 
thus making the two waves more nearly equal to the natural period 
of each circuit, but there may be more losses on this account. 


127. The aerial wire with which the open-circuit inductance is con- 
nected, is shown diagrammatically in the forms preferred by different 
inventors, in figs. 51a, b, c, d, e, f, and g. Certain shapes are found 
to radiate better than others. The best form has probably not yet 
been determined. That now used on board ship is what is known 
as the fiat-topped type. It works well with all forms of closed cir- 
cuits here' shown, and is easily understood from the photograph 
(PL II) and from the description given in Appendix B. 

Connection with wires to operating room may be made at either 
end or at the center, and at shore stations leads may be taken from 
both ends. Where leads are taken from the center, as in fig. 51e, 
both ends of the flat-top are subject to high potentials. Where 
taken from one end the free end is subject to high potential, as in 
fig. 51f. Where leads are taken from both ends the highest poten- 
tial is in the center of the flat-top, as shown in fig. 51g. One advan- 
tage of the last method of connection is that the wires, where they 
are supported, do not need to be as highly insulated as when the 
highest potential exists at one of the ends. 

It is not generally convenient on board ship to take leads to oper- 
ating room from both ends, so that the aerial shown in fig. 51g is 
more useful on shore. 


128. It will be noted in figs. 41 and 42 that the De Forest and 
Shoemaker aerials are constructed so as to form a loop beyond three 
spark points arranged in the form of a triangle, and that the lead 
from the inductance is connected to one of these points. 

These spark points form what is known as an anchor spark gap. 
The gaps are so short that the high potential currents used in send- 
ing easily pass over them. Both sides of the loop are at the same 
potential, and the maximum potential is reached at the middle of 
the cross connection at the top. The receiving circuit is connected 
to the two ends of the loop above the anchor spark gap and the loop 
thus continued to the tuning coil. The receiving potentials are too 
low to cross the gap, so that it serves as a cut-out for the sending 
current when receiving. A single gap is used in the Slaby-Arco 
sets for this purpose. 

The loop in the flat-topped aerial is arranged in various ways. 
These arrangements do not affect the use of the aerials for those 
forms of tuning coils which are constructed for receiving in other 
than a looped circuit. For such tuning coils the two sides of the 
*oop are simply brought together and used as one wire. 


129. Except where they pass near conducting objects or through 
decks, all parts of the aerial wires are left bare. This probably 
detracts very little from their efficiency as radiators, and is more 
convenient on account of the lighter weight and smaller surface 
exposed to wind pressures as compared with insulated wires. 

The size generally used is made up of 7 strands of No. 20 B. & S. 
phosphor or silicon bronze wire having fairly high elastic strength. 

Wire, composed of strands having much greater surface than solid 
wire of the same size, offers less resistance to high frequency currents; 
it is also more flexible. Its elastic strength is sufficient to prevent 
permanent elongation and consequent sagging, to the extent shown 
by pure copper wire. A detailed description of the method of con- 
struction of fiat-topped aerials for given wave lengths, as followed 
at the New York yard, is given in Appendix B. 



130. The large momentary currents in aerials produce large induc- 
tive effects in conductors near, and parallel to them, and thus cause 
waste of energy. This is more noticeably the case when the conduc- 
tors, such as wire stays, shrouds, braces, etc., have nearly the same 
electrical length as the aerial. On this account rigging, subject to 


induction on account of its proximity to the aerial, is divided into 
short electrical lengths by choke coils made of No. 26 B. & S. soft iron 
^vire served around them for a length of about 10 feet. Rigging near 
the aerial is set up — and thus insidated from the hull — by hemp 

Greneral instructions to provide against losses due to these induc- 
tive eflFects are given in the Appendix. 

Special care is taken to secure good insulation of the aerial where 
it passes through decks and where it enters the operating room. 

It should be noted that an aerial wire, parallel and near to a long 
lighting or power lead, may induce sufficiently liigh potentials in the 
lead to puncture the insulation of the dynamo armature or cause 
sparking between the lead and other conductors in the vicinity of 
combustible material, thereby causing fires.' Both of these effects 
have been experienced. They are especially frequent and dangerous 
to motor generators in operating rooms, and it is on this account that 
the protective devices shown in standard diagram for installation of 
wireless-telegraph sets (fig. 72, etc.) are installed. Care should be 
taken in installing sets to see that low and high potential leads are not 
parallel or near to each other at any point. 


131. On board ship the ground lead is weU soldered to some portion 
of the hull. At shore stations it is connected either to copper plates 
in contact with moist earth, fig. 78, to radiating lines of galvanized- 
iron telegraph wire ending in pipes driven to moist earth, fig. 79, or 
to wire netting spread on the surface of the ground. 

The exact function of the *^ ground^' in wireless telegraphy is some- 
what obscure (see par. 123); but it is well settled that large area of 
good contact with moist clay furnishes the best ground. 

Except where the station is built close to the permanent water 
level and the ground plate can be kept below that level at all times, the 
ground formed by radiating lines of galvanized-iron wire connected 
to pipes is usually the most satisfactory. This differs Very little from 
the wire-netting "ground,"' whether laid on the earth or supported 
at a distance above it. In the latter case it acts upon and is acted 
upon inductively by the earth. 

Where and when the soil is very dry, it is necessary to pay much 
greater attention to the ground connections, and at some stations 
arrangements are made for supplying water to the ground plate. 

132. It is noted that where the resistance of the earth in the vicinity 
of the station is high, the station is a poor radiator. At such stations 
radiation can usually be improved by increasing the size of the arti- 
ficial ground. 


132a. An oscillator formed of a straight wire free at both ends \\sls 
high potentials at both ends, and its electrical period is equal to twice 
its length. 

An oscillator formed of a vertical wire free at one end and attached 
to the earth at the other, has high potential at the free end only if the 
earth connection is good. If it is not good, the tendency is to choke 
the current passing in and out of the earth, and thus to cause a rise 
of potential and consequent sparking at the earth connections. 

The natural period of such an oscillator, which should be approxi- 
mately four times its length, is, on account of the choking effect of the 
poor ground shortened and made irregular, and the sending qualities 
of the station thereby impaired. 

It is found that the resistance of the earth between two similar rods, 
driven into it to the same depth, at the same distance apart, varies 
widely in diflFerent localities, the resistance at some places being as 
much Ls 20 times greater than at others. It varies continually with 
the moisture and probably with other conditions near the surface. 

Low-ground resistance at Ji station is usually accompanied by good 
radiating qualities. 

Ample surface on lead to the ground from the sending inductance 
and good electrical connection with the ground wires or plates are 
essential on account of the large momentary currents created when 
sending. (See par. 88.) 


133. The efficiency of our means for electric wave making is diffi- 
cult to determine. Estimating that 50 per cent of the energy in each 
condenser discharge is dissipated in light, sound, and heat in the 
closed and open circuits, we have in a condenser capacity of 0.02 nif . 
charged to a potential of 30,000 volts, the remaining 50 per cent of 
6.64 foot-pounds = 3.32 foot-pounds of energy sent out in each wave 
train. This is equal approximately to 45,000,000 ergs per wave train, 
and it has been estimated, as stated in paragraph 88, that the most 
sensitive electric wave detectors require to operate them approxi- 
mately 0.007 erg per dot. We have also the statement that the energ}" 
in any part of the wave train varies inversely as the square of its dis- 
tance from the sending station. In other words, the strength of 
received signals should be four times as great at 100 miles as at 200 


134. In practically all cases the same aerial wire is used for send- 
ing and receiving both at ship and shore stations. 

The advancing lines of electric and magnetic force cut the aerial 
wire and induce in it alternating currents of the same period as 
those in the sending circuits. 

If the receiving aerial has a natural period equal to that of the 


passing waves, the currents in it will rise, until the energy received 
per wave is equal to that dissipated. 

If the receiving aerial is directly or inductively connected to a 
closed oscillating circuit to which nearly all the energy received 
per wave is transferred at each half period, instead of being re-radi- 
ated, as would otherwise be the case, the closed oscillating circuit 
will absorb the energy, and if its period is equal to that of the 
arriving waves the oscillations will increase in amplitude with each 
transfer of energy. If a detector is placed in this circuit, and the 
maximum amplitude of the oscillation set up is sufficient to make it 
function, the passing of groups of wave trains, separated into dots 
and dashes at the sending station, can be detected at the receiving 

At the sending station the closed circuit furnishes energy to the 
radiating circuit, which sends it out in the shape of electric waves. 
At the receiving station the radiating circuit absorbs this radiated 
energy and transfers it to the closed circuit. It is evident that no 
spark gap is required in the closed receiving circuit, and that since 
no high potentials nor heavy currents need be provided for, it is not 
necessary that the receiving circuit should have the same dimen- 
sions or arrangement as the sending circuit; but in all other fea- 
tures receiving circuits are the exact analogue of sending circuits, 
with the detector in place of the spark gap. The detector can be 
placed in the spark gap of a sending circuit and the latter used as 
a receiving circuit, but it is not convenient to do so, and it may be 
in some respects less efficient than a receiving circuit specially 

135. None of the direct-connected sets already described were 
originally designed to permit the coupling to be varied without vary- 
ing the wave length of either the open or closed sending circuits, 
but they are all now fitted in that way, and it is found desirable to 
cormect receiving circuits in the same way. 

136. All close-coupled sets send out two waves, one shorter and 
one longer than the natural period of either circuit. It is possible 
to adjust the receiving circuits so that they respond better to one 
of these waves than to the other, but the best results are obtained 
when the open and closed receiving circuits have the same natural 
periods and the same coupling as sending circuits. Sender and 
receiver are then in resonance, and the latter will respond better 
than when tuned to but one of the two waves. 

It is more difficult to determine the coupling of receiving than of 
sending circuits, and also to measure the natural period of such cir- 
cuits. The high resistance of some receiving circuits prevents their 
having a pronounced period of oscillation, and on this account varia- 
tion of coupling is not always considered in tuning receivers, and 
they are usually adjusted to but one of two waves. 



137. The Slaby-Arco receiving circuits are shown in fig. 37. They 
consist of a variable inductance in the open circuit and a fixed con- 
denser, variable inductance, and detector in the closed circuit. The 
construction marked "D*' (fig. 37) will represent the detector in 
all diagrams. A condenser of considerable capacity is sometimes 
placed in parallel with the detector in these chtjuits to prevent the 
change of capacity in the detector from greatly affecting the period 
of circuit. 


138. Fig. 37 also serves to represent the Massie receiving circuits, 
which are the same as the Slaby-Arco. 

The only difference between the Slaby-Arco and the Massie send- 
ing circuits, as will be seen by an inspection of figs. 32 and 33, is 
the unimportant interchange of relative position of transmitting 
condenser and spark gap. The receiving connections are alike in 
principle though not in appearance. 


139. The Telefunken receiving circuits of the latest type are con- 
nected for what is called plain aerial, as in fig. 40, or inductively 
connected with variable condenser in the closed circuit, as shown in 
fig. 40a. The inductance is also variable in steps. Provision is 
made for direct connection if desired. When inductively connected 
the coupling can be varied at will by adjusting the distance and 
direction of the two coils K and M from each other. 


140. The Fessenden receiving circuits are shown in fig. 38. They 
are direct connected, with variable roller inductance and fixed con- 
denser. When it is desired to prevent interference from other sta- 
tions using wave lengths not greatly different from the ones it is 
desired to receive, a special type of inductive connection, called an 
interference preventer, is used. This is shown in fig. 38a. 

This gives two paths to ground for the induced current from the 
aerial. Each one of these is variable at will, and at the same time 
the period of the circuit formed by the two fixed inductances and 
two variable capacities can be kept constant, and equal to the wave 
length it is desired to receive, while the waves it is desired to exclude, 
pass through one path or the other to ground. 

This interference preventer works well in practice. 


141. The Stone receiving circuits are shown in fig* 39. They are 
inductively connected, with variable condensers and fixed indue- 


tances. The latter, however, are. movable as a whole, so that the 
coupling can be varied at will. 

Inspection of fig. 39 will show that the Stone set has a variable con- 
denser, in parallel with a fixed inductance (A), below the variable 
inductance (B), in the aerial leads, and that an additional closed cir- 
cuit (C), with fixed inductance and variable condenser, is interposed 
between this direct-connected circuit (A) and a second closed circuit 
(D), with two variable condensers, one in series and one in parallel 
with the detector. .^-^ 

The circuit marked (C) is called a weeding-out circuit j and it is used 
in connection with (D) when sharp tuning is necessary to prevent inter- 
ference. Provision is made for cutting out circuit (D) and placing 
the detector in circuit (C) when sharp tuning is not necessary. 


142. The De Forest and Shoemaker receiving connections are 
shown in figs. 41, 41a, 42, and 42a. 

They are alike in general principle, but differ considerably in the 
actual arrangements, the original idea being not to tune the receiving 
circuit to the same wave length as that emitted by the sender, but to 
set up stationary waves in a closed receiving circuit grounded at one 
point and having a period equal to some multiple of the wave length 
it is desired to receive, and, by changing the relative positions of the 
inductances and capacities in the receiving circuit, change the position 
of the nodes and loops of current and potential in the stationary 
waves, and thus bring the coherer detector to a potential loop, or the 
electrolytic detector to a current loop. 


143. Inspection of the elementary diagrams of sending and receiv- 
ing circuits discussed, shows that the sending circuits vary little from 
two common types — the direct and the inductively connected. Each 
is composed of a standard, closed, oscillating circuit forming part of, 
or inductively connected to an open radiating circuit, with provision 
for changing the natural period of both circuits. 

The receiving circuits are seen to be, in general, the coimterpart of 
the above, with the detector in place of the spark gap. It is found 
that when, for the purpose of obtaining greater selectivity, and thus 
comparative immunity from interference from waves whose period 
diflfers somewhat from that of the receiving circuit, the latter is made 
more complicated, as in the Fessenden interference preventer, fig. 38a, 
and the Stone weeding-out circuit, fig. 39, the range of reception is 
somewhat decreased. 

We attain great selectivity but lose sensitiveness. There is a loss 
of energy in the various transformers. Signals which can be per- 


ceived when the simpler connections are used, are inaudible when the 
arrangements necessary to secure great selectivity are in use. 

Direct-connected sets are usually considered the stronger for send- 
ing, but the best results have been obtained where the number of 
turns common to the two circuits is less than one turn; in other 
words, when the mutual induction or coupling is very loose, and the 
lengths of the two waves produced, so nearly aUke that they can not 
be distinguished in the wave meter. 

Equally good results are obtained when the coupling between induc- 
tively connected sets is just loose enough to bring the two waves prac- 
tically together. Such sets of either type should have loose coupled 
receiving circuits. 

All wireless-telegraph sets installed on board ship or at shore sta- 
tions are so fitted that the throw of a single switch disconnects the 
sending circuits from, and connects the receiving circuits to the 
aerial, and vice versa. The use of this switch prevents damage to the 
receiving apparatus, which would result by sending while it is con- 
nected to the aerial. 


144. The four types of detectors in general use include coherers 
and microphones (usually considered as imperfect contact or voltage 
operated detectors), magnetic and electrolytic (usually considered as 
current-operated) detectors. 

Of these four types all are self-restoring, except the first, which 
requires tapping or some other mechanical shock to restore its sensi- 
tiveness after cohering. All, except the first, are used in connection 
with a telephone. Their sensitiveness depends largely on their adjust- 
ment, but when properly adjusted it is inversely as the order in which 
they are given above. Microphonic detectors are not extensively 
used in the Navy, and magnetic detectors practically not at all. The 
coherer, at present is largely used as an auxiliary, the great majority 
of wireless-telegraph sets being fitted with some form of the electro- 
lytic type in addition. 

Coherer detectors have the great advantage over all other forms 
thus far produced, in that they change under the action of electric 
waves from a nonconducting to a comparatively good, conducting 
state, and in this condition permit the passage of sufficient current to 
ring a bell and thus attract attention. The change in conductivity, 
and consequently in the current passing through the other forms of 
detectors, is so slight, that cU efforts thus far to create visible mechan- 
ical movement by means of this change have been unsuccessful at any 
great distance, and the only means of utilizing them is in connection 
with telephones. 

The detector, in addition to forming part of the closed receiving cir- 


cuit, has its terminals connected to a local circuit containing a source 
of current (usually one or more primary cells). The alternating cur- 
rents induced in the closed receiving circuit change the resistance of 
the detector, and thereby change the current in the local circuit, pro- 
ducing a sound in a telephone, or causing a movement of b relay 
tongue which closes another circuit, in which is the hell and Morse 


146. Before describing the connections and accessories of the vari- 
ous types, it may be well to note that data on the duration of the effect 
on a self-restoring detector, of a wave train lasting a given time, is 
almost entirely lacking, though it is of importance, as determining the 
interval it is possible to have between wave trains, and yet make their 
effects cumulative, both on the detector and on the ear. 

For instance, it was shown in paragraph 96, that when sending at 
such speed that the duration of a dot is 3^5 of a second, using 60-cycle 
current, with a spark gap set at maximum potential distance to give 
but one wave train per alternation, a dot is made up of 8 distinct 
wave trains, each lasting approximately jjni^ffirir of a second and sepa- 
rated by an interval of ^K ot a second. In other words, that the inter- 
val between wave trains is nearly one hundred times as long as the 
duration of one train, and that about 50 foot-pounds of energy is 
expended per dot when utilizing 2 kilowatts. It is a question 
wliether the 50 foot-pounds available produces the loudest signals 
when sent out in 8 wave trains of a certain amplitude. It is possible 
that with the same power concentrated in 4 trains of greater ampli- 
tude, or diffused in 16 trains of lesser amplitude, louder signals might 
be produced. It was pointed out in paragraph 97 that a frequency 
as low as 7i cycles would give gne wave train per dot and two per 
dash at the sending rate given, so that it is quite probable that some 
other frequency than 60 cycles per second will give better results in 
the receiving apparatus. 

It should also be noted that the energy in a wave train depends on 
the amplitude and number of its oscillations. The effect on 'the 
detector being cumulative, there is probably some number of oscilla- 
tions per train, which is most efficient. Therefore in considering the 
action of electric-wave detectors we should look upon it as being pro- 
duced by electric toai^e trains of a certain number of oscillations or 
waves per train, and a certain number of trains per second, or per dot, 
and the ihost efficient use of any given power will l)e made when the 
energy is best distributed, both in any train and in the number of 
trains per second. 

146. A telephone diaphragm receives impulses from the pulsating 
current produced by the constant E. M. F. and varying resistance in 
2740—06 6 


the detector circuit. It responds only to entire wave trains, and not 
to particular waves, and only to groups of wave trains if the latter are 
very close together, so that, generally speaking, we may say that the 
pitch — that is, the number of vibrations per second of the sound heard 
in a telephone — is that, due to the number of alternations or interrup- 
tions of the primarj^ sending circuit per second. 

By distributing the available energy over a greater number of wave 
trains per second, a breaker sound but a higher rioU is produced. 

The human ear is not equally affected by sounds of equal loudness, 
regardless of their pitch. 

The note of a 60-cycle alternator is an octave above that of a mer- 
cury turbine interrupter, making 1,800 revolutions per minute, and 
having a two-segment ring — that is, two breaks per revolution and 
sparking only on the break. The higher frequency produces a more 
piercing spark, one that can be distinguished farther than the one of 
lower frequency, though probably of greater intensity. 

In order to get the very best results the frequency used sliould be 
that to which the operator's ear and the telephone diaphragm are 
most sensitive. Telephone diaphragms which will respond best to 
sounds if a particular frequency can be made. 

147. Resonance is thus seen to be a highly important quaUty iii 
wireless-telegraph circuits. (1) Resonance of primary alternator fre- 
quency with secondary of transformer and capacity in closed circuit; 
(2) resonance of closed oscillating circuit, with open radiating cir- 
cuit; (3) resonance of coupled receiving circuits, with coupled send- 
ing circuits; (4) resonance of telephone diaphragm with primary fre- 
quency; (5) resonance of human ear with telephone diaphragm. All 
these are changeable at will except the last, which can not be changed, 
and is different for different people. Experimental data on this sub- 
ject are exceedingly limited, but such as we have indicate that the 
average human ear is most sensitive to notes of higher frequencies 
than those thus far generally used in wireless telegraphy. 


148. The coherer detector used with the Slaby-Arco sets is shov^ii 
in fig. 52. It consists of an exhausted glass tube containing two silver 
plugs fitting snugly in the tube. These plugs have well-polished, 
slightly sloping ends. The wedge-shaped space between the two plugs 
or electrodes varies from 2 to 4 millimeters in length and contains fil- 
ings of oxidized nickel-silver alloy. A great many other kinds and 
mixtures of filings have been used but without better results. 

The plugs are connected to metal caps on the ends of the coherer by 
platinum leading-in wires. 

The coherer is slightly adjustable in sensitiveness by turning the 
point of the wedge up or down. It is most sensitive with the point 


down, but this is not necessarily the best working position. Coherers 
vary materially in sensitiveness and in the conditions under which they 
^vill work best. Their sensitiveness depends on the size, amount, 
and degree of oxidation of the filings and the distance between the 
electrodes. Their sensitiveness changes somewhat with age and use. 

The least sensitive ones are usually the best for short distances, 
while they may not work at all at distances at which more sensitive 
ones work well. 

They offer a very high resistance to the passage of very low voltage 
current. This resistance can be broken down by a certain voltage or 
potential called the critical potential, which is usually about 1.5 volts. 
When so broken down, the resistance of the coherer for steady current 
is between 2,000 and 3,000 ohms. When tapped or shaken the filings 
resume their nonconducting character. The electric induction 
between the filings when above a certain amount brings them together 
and they form conducting chains, which are broken by being shaken 
or tapped. When thus brought together the filings are said to cohere, 
hence the name coherer. The tapper, which is usually an electric bell, 
is called a decoherer. 

Coherers when used continuously become magnetized and do not 
decohere easily. They will recover their normal state if allowed to 
rest for a few days. 

Their action lacks uniformity, because at every tap of the decoherer 
the filings assume new positions, which may or may not be as well 
adapted for cohering as other positions. 

Coherers should be tested out as opportunity offers and marked as 
useful for long or short distances, as the case may be. When not in 
use, they should be kept in their box and away from the vicinity of the 
strong magnetic fields in the neighborhood of the sender. 


140. Fig. 43 is an elementary diagram of detector connections in the 
Slaby-Arco sets. 

In this diagram R represents a relay, T a relay tongue, D a deco- 
herer, and M the magnets and armature of a Morse writer. By trac- 
ing the connections it will be seen that a circuit commencing at one 
terminal of the detector passes through a single primary cell to the 
tapper of the decoherer, thence through the relay magnets to the bot- 
tom of the receiver tuning coil, and is completed through this coil to 
the other terminal of the detector. A second circuit, containing four 
primary cells, passes through the decoherer magnets and is broken at 
the relay tongue. Its other leg passes through the Morse-writer mag- 
nets to the relay tongue. 

It will be seen that the second circuit will be closed by a movement 
of the relay tongue to the right and that the first circuit will be opened 
by a downward movement of the tapper. 


The decoherer and Morse writer are shown in series in the second 
circuit for simphcity. They are usually connected in parallel. The 
single-cell circuit is completed through the tuning coil in the sets as 
furnished, but it can be connected with equally good results direct to 
the other terminal of the detector. 

A general statement can be made to the effect that the local circuits 
for receiving signals through any type of detector are shunted directly 
across its terminals. 

PL III is a photograph of a complete receiving instrument. 

The relay is a Siemens polarized relay wound to a resistance of 4,QO0 
ohms. It >\nll work on the current produced by a single cell through 
a resistance of 60,000 to 80,000 ohms. 

160. Thfe Morse v>riter is fitted with clockworkfor reeling off the tape, 
with an inker or printer for making the dots and dashes, and with mag- 
nets, whose armature, when attracted, starts the clockwork and lifts 
the inker against the tape. When released, the armature drops the 
inker and stops the clockwork. 

The four primary cells furnish sufficient current to actuate the deco- 
herer armature and Morse-writer armature at the same time. 

The first circuit will be called the coherer circuit, the second the deco- 
herer circuit. 

The critical potential of the coherer is higher than that of the single 
primary cell in the coherer circuit, so that the coherer remains in the 
nonconducting condition until the increase of potential due to the 
alternating currents produced by the passing electric waves equals the 
critical potenlialy when its resistance drops to from 2,000 to 3,000 ohms 
and current from the single cell energizes the relay magnets in the 
coherer circuit. The relay tongue T at once closes the decoherer circxiit. 
The current in this circuit energizes the Morse-writer magnets, its 
armature starts the clockwork, and presses the inker against the tape. 

At the same time the same current energizes the magnets of the deco- 
herer and the armature of the latter pulls the tapper down, thereby 
brealcina the coherer circuit and tapping the coherer. 

The relay tongue T immediately opens the decoherer circuit. The 
decoherer armature flies back and the Morse writer armature drops the 
inker and stops the tape. Everything is in readiness for anothei 

The connections above described provide for breaking the coherer 
circuit at the decoherer tongue prior to tapping the coherer, thus pro- 
tecting the latter from the spark at break. They also provide for 
breaking the decoherer circuit at the relay. This circuit has an E.M.F. 
of six volts, and the self-induction of the decoherer and Morse writer 
magnets is large enough to produce a spark at break sufficient to 
injure the relay contacts. 

In the coherer circuit the self-induction of the relay magnets is 


large, but there being but one cell in the circuit the spark at break is 
smaller, so that connections are now made to break the decoherer dr- 
cuit at the tapper like an ordinary electric bell and break the coherer 
circuit in the coherer. 

151. When a dash is made, several movements of the decoherer and 
relay take place in quick succession. In order to prevent a dash from 
appearing as a succession of dots on the tape, the movement of the 
Morse writer armature must be sluggish enough not to release the 
inker during the rapid interruptions of current when receiving a dash, 
but quick enough to release it during the interval between dashes and 

When sending rapidly, the intervals between the elements of letters 
are shortened and a point may be reached where, though the coherer 
may function properly, the mechanical movements in the Morse 
\\Titer are too slow, and a continuous mark is made on the tape. 

It is for this reason (though the qualities of different instruments 
vary) that a receiving speed of about 20 words a minute is generally 
the limit of tape recorders, while more than double that number can 
be received by sound. 

The relay, decoherer, and Morse vo-iter are all interdependent and 
must all be adjusted together, or readable signals on the tape can not 
be produced. Detailed instructions for their adjustment are given in 
Appendix D. 

162. A well-adjusted relay will work when the coherer is bridged by 
two fingers of one hand, one finger on each cap of the coherer. 

For testing the sensitiveness of the complete receiving instrument 
and its readiness for receiving a buzzer is furnished. The short elec- 
tric waves sent out by the buzzer aflFect the coherer, and consequently 
the relay, at short distances. The relay should be dead-beat, as well 
as sensitive — i. e., it should not chatter. 

To prevent injury to the relay contacts when the decoherer circuit is 
broken, either intentionally or accidentally, a battery of five polariza- 
tion cells in series is shunted around them. These are secondary cells, 
having dilute sulphuric acid as an electrolyte and platinum wire elec- 
trodes. They polarize very quickly on sudden increase of current, but 
partially prevent the spark at break. 

It was not kno^n at the time these sets were constructed that these 
polarization cells, if one of the terminals is made very fine, are much 
more sensitive detectors than the coherer in connection with which 
they are used. 



168. The switch referred to in paragraph 134 for changing from 
sending to receiving and vice versa is shown in PI. III. It is a mul- 
tiple, double-throw switch. 


When in position for receiving, the primary sending circuit is 
broken, so that pressing the sending key does not close the circuit. 
When thrown into position for sending, the multiple switch closes the 
break in the primary sending circuit, breaks the connection between 
receiver, tuning coil, and aerial; breaks coherer connections to closed 
receiving circuit at both ends of coherer; breaks decoherer circuit on 
both sides of relay tongue and coherer circuit, near relay magnets. 
These circuits are broken to protect them from induced high potentials, 
due to the vicinity of the sending circuits. 

In some receiving instruments the coherer is lifted to a vertical posi- 
tion when the multiple switch is thro^Ti to the sending position. The 
filings in this position separate entirely from the upper electrode, and 
the coherer is thus more eflFectively protected. 

When receiving circuits are inductively connected, as in the Stone 
sets, a special switch for throwing from sending to receiving is not 
required. It is, however, necessary to protect the detector, and the 
Stone sets are fitted with an ingenious and useful device for this pur- 
pose, whereby an attachment to the sending key breaks the detector 
circuit just before the sending key makes contact. When the sendin«j 
key is released the receiving circuit is automatically cut in. The oper- 
ator always wears his telephone while sending, and the receiving station 
can ^' break" him in the middle of a word or message by a call, which 
he can hear in the intervals between his own dots and dashes. 

This will be referred to in the description of the Stone circuits. 

164. Various methods of revolving coherers have been proposed and 
us^d to a certain extent. 

When the filings in a revolving coherer are made conducting bj- 
the impact of electric waves on the aerial, they are immediatelj- 
decohered by their own weight so that they are in a sense self-restor- 
ing and can be used in connection with a telephone. 


166. The other types of detectors in use are self-restoring. The 
simplest of these is the Massie microphone (or oscillaphone, as it is 
called by the inventor), which consists of a needle held in light con- 
tact as a bridge between two pieces of carbon. Where there is no 
motion the needless own weight is sufficient to make conta<5t. On 
board ship a permanent magnet holds the needle in place against all 
but very violent shocks. The carbon edges should be kept sharp 
and needle bright. 

Fig. 44 is an elementary diagram of the microphone connections, 
and PI. IV is a photograph of a complete receiving instrument. 

If fig. 44 is compared with the preceding fig. 43, showing the Slaby- 
Arco detector connections, it will be seen that the Morse writer and 
decohe/er circuit does not appear, that a telephone has taken the 


place of the relay, and instead of having a single cell in the telephone 
circuit there are two or more in circuit with a variable resistance, 
which permits the voltage at the terminals of the microphone to be 
varied until the "critical'^ potential is reached. Also that the tele- 
phone circuit, unlike the coherer circuit in the Slaby-Arco sets, is not 
in series with the tuning inductance, but is shunted directly around 
the microphone. 

The carbon steel microphone, of which this detector is a type, is 
usually classed among imperfect contact detectors, but it is self- 
restoring and its change of resistance is not sufficiently great to work 
a relay so that its use is restricted to the telephone. Receiving cir- 
cuits having telephones are simpler and much easier to keep in adjust- 
ment than those with the relay and Morse writer. 

156. All detectors of the microphone type are somewhat irregular 
in their action and more or less unsatisfactory^ on that account. 
They are considerably more sensitive than the coherer and generally 
less sensitive than detectors of the electrolytic type about to be 
described. They can occasionally be used to advantage when more 
sensitive detectors can not. Their reliability is improved in the 
Father Murgas type by using a number of detectors in multiple and 
revolving the needle (in this case a small steel shaft) slowly by clock- 
work. This produces a very weak, musical note in the telephone, 
which does not interfere with the reception of messages, while the 
constant change or renewal of contacts keeps the instrument always 
in operative condition. 

Like the coherer, the microphone becomes conductive at a critical 
potential, just below which it is kept by the use of the potentiometer 
in circuit. The slight increase of potential caused by the induced 
currents in the aerial changes its resistance enough to produce a 
sound in the telephone. 

By adjusting the potentiometer to a point just below which a 
frying sound is heard in the telephone, the microphone is kept close 
to the critical potential at all times and thus in its most sensitive 

It is to be noted, as pointed out by Prof. Oliver Lodge, that the 
attraction between electrified bodies varies as the square of the dis- 
tance, and that the unit of distance is 1 centimeter. Between bodies 
so close together that the distance between them can not be measured, 
the attraction may be very pronounced even though the diflFerence 
of potential is very small. 

167. The multiple switch on the Massie sets when changed from 
receiving to sending closes the primary sending circuit, breaks the 
lead from receiver to aerial and also breaks the battery circuit. 

As a "cair^ in connection with the microphone a coherer with tap- 
per and relay is furnished. The relay closes a circuit containing an 


alarm bell. The limit of this ''bell alarm" is determined by the sen- 
sitiveness of the coherer with which it is connected. It is useful only 
when working with a station within its radius. 


168. Fig. 45 shows the detector connections of the Fessenden sets 
and PL XXIII a complete set of sending and receiving apparatus. 

The detector is of the electrolytic type and consists of a fine plat- 
inum wire, just touching an electrol}i;e made either of a 20 per cent 
solution of nitric or sulphuric acid, or an alkali. Of these nitric acid 
is preferred. The other terminal of the detector is also platinum. 
The containing cup is made quite small so that the cohesive power 
of the electrolyte will prevent splashing in a seaway. 

This detector is self-restoring. Its change of resistance on the 
impact of electric waves is so small that the increased amount of 
current in the local battery circuit will not work a relay except when 
the signals are ver^' strong. It must be used with a telephone. 

An examination of the detector connections in fig. 45 shows that, 
except in the arrangement of the potentiometer resistances, they 
are the same in principle as those of the Massie sets. The electro- 
lytic detector must, however, have the Jine wire terminal (if but 
one terminal is fine) connected to the positive pole of the local bat- 
tery, as shown in fig. 45, otherwise the device is not operative. If 
both termiJials are fine or comparatively small in area, it makes no 
difference which is anode and which cathode; but the^TW^r the anode 
or, rather, the smaller the area of the portion m contact with the 
electrolyte, the more sensitive the detector. Wire less than 0.0004 
of an inch in diameter is used for detector points. At the same 
time an efficient and nigged detector for short distances can be quickly 
made from a 1 or 5 candlepower incandescent lamp by breaking a 
hole in the bulb, removing the filament, and covering the leading-in 
wires with the solution referred to above. 

This form is called the Delaney lamp detector, having been invented 
by Chief Electrician Delaney. 

The extremely fine, almost invisible, wire used when great sensi- 
tiveness is required in order to pick up weak signals is easily burned 
out, and for nearby signaling the Delaney detector is very useful. 

The platinum wire is dra>\Ti down to the extreme fineness referred 
to by being worked with a larger silver wire, of which it forms the 
core. The silver wire surrounds and protects it. Before using, the 
silver wire is removed by immersion in strong nitric acid. 

The '^ point'' thus made is clamped in a holder over the detector 
cup. The position of the holder is adjustable vertically by a screw, 
so that the immersion of the point can be varied at will. 

169. In the hands of expert wireless operators the bare wire thus 
adjusted is found to be slightly more sensitive than any other form 


of detector thus far developed, but to keep the proper adjustment 
requires constant attention. The results of experiments by Doctor 
Ives are to the eflFect that with 0.04 mil wire a depth of immer- 
sion of 3 mils gives the best results. 

A much more convenient method of using this detector is to seal 
the fine wire in a glass tube, leaving only a minute portion of the 
end projecting. Neither nitric nor sulphuric acid affects glass, and 
since platinum and glass havmg the same coefficient of expansion a 
perfect joint can be made between them, so that no capillary action 
occurs to increase the area of contact between the platinum point 
and the electrolyte. On this account the depth of immersion of 
glass points is not of great importance. 

This detector was first called a liquid barretter^ but has received 
the name electrolytic detector because it is electrolytic in its action. 

160. When a current flows through an electrolytic cell the electro- 
lyte is decomposed and oxygen is liberated at the anode. This gas 
is a nonconductor and its accumulation at the anode interferes with 
the passing of the current. This action is called polarization. A 
complete explanation of this action has not yet been given. 

The potential of the battery in 'the detector circuit produces a 
current through the detector until enough oxygen accumulates 
around the fine wire anode to insulate it. The critical potential of 
the electrolytic detector is just below that necessary to break down 
this insulating or nonconducting layer of oxygen, and is determined 
by increasing the potential at the detector terminals by means of 
the potentiometer until a bubbling or hissing sound is heard in the 
telephone, then resistance is cut in until this sound just ceases. Any 
increase in potential above the critical potential, such as that due to 
the alternating currents induced in the aerial by electric waves, will 
break down the polarization layer and start a current in the detector 
circuit, which will make a short or long sound in the telephone 
according to the number of wave trains passing. Aa soon as the 
additional potential disappears the detector is again polarized, the 
current ceases, and the detector is ready to receive another signal. 

This rapid self-restoring quality of the electrolytic detector and 
microphone enables them to receive signals as fast as they can be 
sent. When the electrolytic detector is depolarized, gas bubbles are 
set free from the fine wire anode. To facilitate this action hook- 
shaped glass points have been made with the end of the fine wire 
pointing upward instead of downward. No definite increase of sen- 
sitiveness has been noted on this account. 

When in use any drop of potential in the local battery circuit wil 
decrease the sensitiveness of the detector by increasing the addi 
tional potential necessary to depolarize it, so that frequent adjust 
ment of the potentiometer is necessary. 


161. In the Fessenden receivers, the buzzer for testing the sets 
readiness to receive is a permanent mounting on the operating table. 

The multiple switch for changing from sending to receiving is 
worked by a lever passing through the operating table. When 
thrown to the sending position this switch breaks the connection 
between receiver and aerial and receiver and ground, closes a shunt 
around the detector, breaks detector circuit near battery, and dis- 
connects both telephone leads. (See fig. 67.) 

When thrown to the receiving position it breaks the connection 
between the sending circuits and the aerial and breaks one leg of the 
primary circuit. 

When the interference preventer is used no change is made in the 
detector circuits but the additional transformation of the received 
energy causes a loss which decreases the receiving range somewhat. 


162. Fig. 46 is an elementary diagram showing the Stone receiving 
circuits and detector connections. PI. XX is a photograph of a com- 
plete set at the Portsmouth Navy- Yard. 

These sets as furnished have, as will be seen from an inspection of 
the figure, the detector circuit completed through the tuning induc- 
tance which, as previously stated, is generally unnecessary, equally 
good results being obtained when connection is made direct to de- 
tector terminals. 

The detectors used with these sets are of the electrolytic tj-pe. 
Provision is made by means of a double throw switch for connecting 
the detector and its accessories, either in circuit C or D, as desired. 
Circuit D is used when interference is to be cut out but the double 
transformation through the weeding-out circuit C causes a loss which 
decreases the receiving range somewhat. 

The glass points used have their upper ends filled with mercur}\ 
Two are mounted together, either of which can be put in circuit by 
means of a movable contact-maker or switch dipping in the mercury. 
Having a spare point ready for use if one is burned out while receiving 
a message results in saving time. 

The material and mounting of this s>\4tch must be of something 
with which mercury will not amalgamate. 

The Stone sets, having only inductive connections between circuits, 
do not require as many precautions for the protection of the receiving 
apparatus from the sender as those previously described. No multi- 
ple switch is required, but the detector is protected by means of the 
sending key which breaks the detector circuit just before making con- 
tact and when contact is made grounds the aerial direct instead of 
through one of the closed receiving circuits. The advantages of being 
able to break an operator at any time while sending are evident. 



163. These are the same in the three and two coil tuner. Fig. 47 
shows the connections in the three-coil tuner and PI. V is a photo- 
graph of a complete receiving instrument. 

An examination of fig. 47 shows that the detector circuit is shunted 
around the detector terminals. The local battery, potentiometer, and 
telephone are in series, as in the Massie sets. A battery switch is fur- 
nished also by which the number of cells in the detector circuit can be 
regulated, one or more being cut in as desired. 

In the De Forest Company's receiving sets the detector and its 
mounting is called the responder. The detector is of the electrolytic 
type. A glass cup is used to hold the electrolyte instead of a platinum 
cup, as in the Fessenden sets. Either bare wire or glass points may be 
used. In detectors of the electrolytic type, when acid is used as the 
electrolyte, care must be exercised in filling the cup to prevent dam- 
age to the mountings from the acid. This is necessary not only on 
account of corrosion but on account of current leaks thus formed 
which weaken signals and rapidly destroy the local battery. All 
electrolytes tend to creep and thus form conducting paths. 

The multiple switch for changing from sending to receiving and vice 
versa breaks the primary circuit when receiving. When sending both 
leads to aerial from receiver and lead to ground from receiver arc 
broken. A second switch o:\ the respoTvder short circuits the detector 
and breaks the local battery current. 


164. The same connections are used for the local battery in the 
fhin aerial as when the receiving circuits are inductively connected. 
The former is shown in fig. 49 and PI. VI is a photograph of an entire 
receiving set inductively connected. 

It will be noted that the local battery and telephone are connected 
directly to the detector terminals and that there are small inductances 
or choke coils in both leads. These are for the purpose of keeping the 
induced currents, due to electric waves, from passing to ground 
through the local battery and telephone and are not absolutely essen- 
tial. The battery consists of five cells, three in parallel and two in 
series, with the usual potentiometer for regulating the potential to the 
critical point at the detector terminals. It will be noted that the 
detector is shunted by one variable and two fixed condensers. These 
can be removed without greatly changing the action of the set. 

Coherer detectors are sometimes connected with a condenser in 
parallel, the object being to give the circuit a definite period inde- 
pendent of the coherer, whose capacity is small but irregularly vari- 
able. By inserting additional capacity the ratio of the coherers' 


capacity to the total capacity in circuit is small, and any change in 
the coherer has less effect on the natural period of the circuit. 

The same reason is given for connecting the condensers as shown 
around the Telefunken detector, which may be of the electrolytic or 
other self-restoring type. 

The Schloemilch electrolytic detector originally supplied with Tele- 
funken sets were hermetically sealed and nonadjustable, only the ter- 
minals for connection to the receiving circuit being exposed. Except 
to regulate the local battery potential the action could not be varied, 
and when for any reason the detector failed to operate the cause could 
not be ascertained. They were not as satisfactory on this accomit as 
the nonmclosed type furnished with other sets and generally not as 

Two types — sensitive and highly sensitive — were supplied. Schloe- 
milch cells are now being replaced with other types. 


166. These are shown in fig. 48, PI. VII, showing a complete receiv- 
ing instrument. 

The Shoemaker detector is of the electrolytic type, but differs from 
all the others io having its own source of potential. It is called hy 
the inventor a primary cell detector. The primary cell has a poten- 
tial of approximately 0.7 volt and consists of a fine platinum wire and 
a zinc rod amalgamated with mercury, both immersed hi a 20 per cent 
solution of sulphuric acid. 

Tlie platinum wire is the positive and the zinc the negative pole of 
the cell. Having its own potential, no local battery is required. The 
telephone is simply shunted across the detector terminals without 
any adjustable resistance, making this the simplest of all det-ector 

The telephone connections are the same for both forms of Shoe- 
maker receiving circuits (figs. 42 and 42a). The platinum-wire ter- 
minal is usually sealed in glass and the sensitiveness of the detector 
is governed like the other types described by the area of the wire 
exposed to the battery solution. 

The zinc rods must be kept well amalgamated and the glass points 
ground off so as to present the end of the platinum wire to the action 
of the hattery solution. 

166. In all electrolytic detectors very strong signals or static dis- 
charges produce actual sparking or an explosive action in the electro- 
lyte, which destroys the platinum point. This is called "burning 
out." In the case of the bare wire reimmersion in the electrolyte is 
necessary. ^Vhen glass points are used, the effect is apparently to 
carry away the wire, so that its end is shrouded by the glass. The 
gas bubble formed by polarization is held in the recess by friction and 
pressure and the detector is inoperative. 


The glass points furnished with the Shoemaker sets are filed off to 
jrive a flat end with the platinum wire flush with surface, and it is 
oc<;asionally necessan^ to tap an otherwise good point to assist the gas 
to escape from the blunt end of the glass. 

Bumed-out De Forest points may be repaired by partially melting 
the glass tip over an alcohol flame until it recedes and exposes a por- 
tion of the wire. The wire thus exposed is cleaned by dipping in 
strong nitric acid and the point is again ready for use. 

It is found that Shoemaker points, after being renewed by filing, are 
improved by cleaning with strong nitric acid. 

167. It is known that polarization due to electrolysis takes place at 
the anode in all electrolytic detectors; but it can not with certainty 
be stated that when the signals are received the breaking down or dis- 
engagement of the gaseous layer is due to its actual rupture. 

In any case, it is known that when the critical potential is exceeded 
the boiling or hissing noise produced is due to tlie changes of resist- 
ance caused by the successive disengagement of gas bubbles. And 
when strong signals are received the disengaged bubbles can be seen 
with a microscope. 

From this point of view, the action of electrolytic detectors is not 
greatly different from that of coherer detectors, except in the matter 
of being self-restoring. 

The electrolyte used has a decided effect on the critical potential of 
the detector and on its sensitiveness. 

It is found by experiment at the New York yard that a saturated 
solution of sal ammoniac between platinum-platinum electrodes has, 
under certain conditions, a very low critical potential and is more sen- 
sitive than the different acid solutions or any weaker solution of sal 
anmioniac. It has, however, the defect of not being immediately self- 
restoring after receiving strong signals and the further practical defect 
of depositing salts, which renders it difficult to operate. 

A slight addition of nitric acid to the sulphuric acid in the Shoe- 
maker solution has been tried with good results. 

The distance between the electrodes in the electrolytic detector also 
affects its sensitiveness. The best results have been obtained with 
a distance of approximately one-fourth inch. 


168. The operation of magnetic detectors depends on the fact that 
when iron is being magnetized its magnetization is somewhat delayed 
in time behind the impressed magnetizing force, and when in this 
condition the iron is very sensitive to any change in the magnetiz- 
ing force, a very small increase of which will produce a momentarily 
large increase in the strength of the magnetic field. This fact was 
investigated and utilized by Prof. E. Rutherford for detecting ek»c- 
tric waves. He published an account of his experiments in 1S9G, 


and since that time many patent-s have been issued for various forms 
of magnetic detectors, the best known and the most largely used of 
which is Marconi's, patented in England in 1902. 

In its present form it consists of a flexible band of silk-covered 
iron wires, moved by clockwork around two pulleys which support it. 
A glass tube, through which the band passes, has a primary winding 
of insulated wire in series with the aerial and a secondary winding 
forming a closed circuit through a telephone. Close to the secondan- 
winding are placed similar poles of two horseshoe magnets, which 
magnetize the iron band slowly moving under them. Electric oscil- 
lations in the aerial, produced by passing electric waves, produce 
momentary changes in the magnetization of the iron band under the 
magnets, and these changes induce oscillating currents in the sec- 
ondary winding which produce sounds in the telephone. 

An elementarA^ diagram of this magnetic detector is shown in fig. 
52b. Like the Shoemaker detector, it requires no local battery, and, 
not being subject to burn-outs except from very high potentials or large- 
currents, it is a very convenient instrument. 


169. A great many other forms of detector have been devised, 
among them the Lodge-Muirhead detector, which is more sensitive 
than any of the filings coherers in use and is adapted to work a 
siphon recorder. 

It consists of a polished steel disk rotated by clockwork, its edge 
just touching the edge of a globule of mercury covered bj^ a film of 
oil. A pad, which rubs against the disk as it revolves keeps it clean 
and bright. 

This coherer may be direct or inductively connected in or to the 
aerial. As stated, its conductivity changes sufficiently to relay a 
current for working a siphon recorder and it has the further advan- 
tage of being self-restoring and can therefore be used with the telephone. 

Other forms of steel mercury detectors are found to be unreliable 
in their action. 

Fig. 52a is a diagram of the Lodge-Muirhead detector described 


170. Constant improvements are being made in the head telephones 
used with self-restoring detectors. 

As has been stated, the change of resistance in these detectors due 
to the passing waves is generally so small that the current change in 
the local circuit can not be made to work a relay. 

The low-resistance telephones in ordinary use are found to be 
unsuitable for wireless work, their windings not having sufficient 


turns to make the weak current affect the diaphragm except at short 

The detector having a high resistance, doubling the number of turns 
of a given sized wire on the telephone magnets does not double the 
resistance of the circuit, and therefore the ampere turns (the magnet- 
izing effect) are increased if the additional turns are eflSciently placed. 

By using wire with very thin silk or enamel insulation wound in 
the most efficient manner close to the magnet cores, and by decreas- 
ing the thickness of the telephone diaphragm, great improvement in 
the reception of distant and weak signals has resulted. 

Pis. VIII, IX, and X are photographs showing particulars of the 
best types of head telephones yet developed. Of these, the type 
shown in PI. VIII is the most sensitive. Specifications relating to 
them will be found in appendix E. The general use of pneumatic 
ear cushions in connection with head telephones has improved recep- 
tion in stations subject to local noises. 

Chapter IV. 


171. By tuning is meant the adjustment of the closed and open 
sending and receiving circuits to the same wave length and to any 
desired wave length within their limits. 

The wave length assigned to a station might be called its tune. 

The standard wave length for ships and shore stations was first 
set at 320 meters; this has recently been changed to 425 meters. 

Three hundred and twenty meters was selected as being near the 
natural wave length of the cage type of aerials with enough induct- 
ance in circuit for the necessary coupling. 

It was found feasible to give the flat-topped aerials now in use a 
longer natural wave length. This enables the power that can be 
effectively used in ships' stations to be increased somewhat, and the 
longer wave length is an advantage when land intervenes between 
the sending and receiving stations. 

Standard oscillating circuits, called vxi've meters, which are adjust- 
able at will to a great number of known wave lengths, are used for 
tuning. When adjusted to resonance ^4th the circuits to be meas- 
ured, the fact is indicated, according to the type of the wave meter, 
either by a maximum glow in a vacuum tube, a maximum move- 
ment of the pointer of a hot wire ammeter, the brightness of a glow- 
lamp, or the maximum reading of an air thermometer heated by the 
currents induced in the wave-meter circuits. 

The open and closed sending circuits are tuned separately. The 
wave meter is set by means of the pointer on its scale to the desired 
V. ave length ; then the inductance in the circuit to be measured is 
varied until a maximum of energy in the wave meter is indicated, a.s 
above. This shows that the two circuits (the standard and the one 
to be measured) are oscillating in resonance and therefore have the 
same period and wave length — namely, that indicated on the wave- 
meter scale. 

The two circuits thus independently timed are then coupled 

After coupling, two points of maximum intensity are generally 
found in the wave meter, indicating by their positions on the scale the 
wave lengths of the two waves sent out. One of these is longer and 
the other shorter than that to which the two circuits were independ- 
ently adjusted. 


For tight coupling, if desired, the mutual induction between the 
two circuits is then varied until the two maxima are at the desired 

If very loose coupling is desired the mutual induction between the 
two circuits is decreased imtil but one sharp maximum is indicated 
by the wave meter. This will be very near the wave length to which 
the circuits have been separately adjusted. 

It will be seen that two senders, in order to emit similar waves, must 
not only have the closed and open circuits in resonance, but they must 
also have the same coupling. 

172. Writers on this subject call the coefficient of coupling the ratio 
between the mutual induction and the square root of the product of 
the self-inductions of the two circuits, expressing it as a percentage. 

If M = mutual induction, 

L = self-induction of one circuit, 
Z*= self-induction of the other circuit. 

The coefficient of coupling according to the above definition 

_ J/. 

None of these quantities can be obtained without very careful meas- 
urements, and therefore the above is of very little practical use in com- 
paring wireless telegraph circuits. If, however, the percentage of 
coupling is called the ratio of the difference in length of the two 
waves sent out to the natural wave length of each circuit, it is easily 

For instance, suppose a close-coupled circuit shows a maximum at 
280 and another at 360 when both circuits are tuned to 320 meters, 

the percentage of coupling by the above definition is ' .^^^ = ^.^.^ = 25 

per cent. 

The percentage of coupUng w^hen but one maximum is found is 
apparently zero. It is in reality very small, but can not be zero as 
long as any energy is transferred from one circuit to the other. 

Whether sending circuits should have tight or loose coupling, or 
tiglit coupling for distance and loose couphngfor selectivity, is not yet 
definitely determined. 

In tuning receiving circuits the wave meter is used as a sender. 
Waves of a definite length, indicated by its pointer, are sent out and 
the position of resonance in the receiver is shown by a maximum of 
sound in the telephone 

By the means indicated above (which will be more particularly 
described later) the wave lengths for the entire range of each circuit, 
both sending and receiving, can be plotted as curves. These are called 
tuning curves. By inspection of these curves the adjustments for the 

2740-06 7 


different circuits can be ascertained and the circuits coupled, both for 
sending and receiving any desired wave lengths. 


173. To render them capable of adjustment, all wireless telegraph 
oscillating circuits have either variable capacities or inductances, or 
both, and provision is also made in most sets for varying the mutual 
induction between related circuits. 

These capacities and inductances vary greatly in design, and those 
for sending circuits, on account of the high potentials used, are very 
different in construction and mounting from those used in receiving 

Both fixed and variable capacities and fixed and variable induc- 
tances are used separately or together. ( It must be remembered that 
any conductor, whatever its shape or position, has both inductance 
and capacity, but the inductances and capacities referred to here are 
those concentrated in coils and condensers, as distinguished from the 
distributed inductance and capacity inherent in the conductors.) 

Variable capacities are of the step-by-step and the sliding type. The 
former have a definite number of variations equal to the number of 
steps, the latter having any number of variations between their highest 
and lowest limits. 

Both types are peculiar to receiving circuits alone, in the sense of 
being movable at will, the capacities in sending circuits usually being 

Variable inductances are of the sliding type, the step-by-step type, 
and the roller type. The sliding type is used almost exclusivel}^ in 
the sending circuits. 

In sending circuits the variable inductance consists of a helix of 
comparatively large, bare wire, mounted on an insulating frame of large 
diameter. The turns are widely separated and are fitted usually with 
three clips or sliders, by means of which connection can be made to 
any point of the helix. This is illustrated diagrammatically in fig. 32, 
PI. XI is a photograph of a large antenna helix, and PL XII is a 
photograph of the Slaby-Arco combined antenna? helix and Leyden 
jar case. 

The closed circuit is permanently connected to one end of the 
antenna helix and the circuit completed by the wire from the movable 
clip, which can be attached to any desired point of the helix. 

The open circuit in direct connected sets has the ground and aerial 
wires, respectively, attached to the other two clips (see fig. 32), and 
these can be attached to such points on the helix as wiU give the open 
circuit the same wave length as the closed, and at the same time give 
the two circuits the number of turns in common necessary for the 
desired coupling. 


In inductively connected sets (see fig. 36) the open-circuit helix is per- 
manently attached to the ground lead, and the antenna lead is 
attached to whatever point is necessary to give the desired wave 
length. The closed-circuit helix is the same as before. 

The mutual induction and coupling are varied by moving the open- 
circuit helix as a whole. 

174. The step-by-step and roller types of inductances are used 
exclusively in receiving circuits. The former is sometimes made up 
with plug steps, giving a limited number of changes, but usually con- 
sists of a cylindrical coil of insulated wire wound on ebonite, glass, or 
other insulating material, one point on each turn being bare. Across 
these points a sliding contact moves, giving as many adjustments as 
there are turns of wire in the coil. (Flat coils of this type have also 
been made by the De Forest Company.) PI. XIII shows the Slaby- 
Arco tuning coil. 

The single-roller type consists of a bare conducting wire wound in 
a spiral groove on an ebonite cylinder. A sliding contact on a rod 
parallel to the cylinder works in the groove and is pressed against 
the wire by a spring. By revolving the cylinder different lengths of 
wire are put in circuit and an infinite number of adjustments can be 

The double-roller type is also adjustable to any desired fineness. It 
has two grooved ebonite cylinders parallel to each other and con- 
nected so as to revolve simultaneously in either direction, reeling the 
conducting wire from one to the other as desired.- On one cylinder the 
turns are insulated from each other, and on the other they are short- 
circuited so that any desired length can be used. 

Single-roller inductances are furnished with Shoemaker sets, double- 
roller inductances with the larger Fessenden sets. They have also 
been used in some Telefimken sets. The earlier Shoemaker sets and 
the smaller Fessenden sets have step-by-step inductances. The De 
Forest, Massie, and Slaby-Arco sets also have the step-by-step type, ' 
varying by one turn of the coil at a time. If the contact touches 
more than one turn at a time, the strength of signals is decreased. 

176. None of the types of variable receiving inductances in use can 
be readily moimted so as to vary the mutual induction between them 
by any definite amount. 

For this reason fixed inductances are used in the closed circuits of 
the Stone and Telefunken receiving sets and the wave length varied by 
the use of variable condensers only. The variable condensers are of 
the sliding type in both these sets, and the circuits have inductive 
coupling, which is varied by varving the distance of the fixed induc- 
tances from each other. 

Closer adjustment of a circuit to a given wave length can be made 
with a sliding condenser or with a roller inductance than with any of 


the other types, but only fixed mductances are suitable for definite 
variations of coupling. 

Since such variations of coupling are necessary, it follows that if 
variable inductances are also necessary an efficient arrangement is 
difficult to devise. 

Where great selecticity is required to prevent interference, a receiv- 
ing circuit should have a very pronounced natural period, and this can 
only be given by a comparatively large inductance. The inductance 
need not, however, be variable, since the variations necessary in the 
wave length can be obtained by the use of variable capacities. 

To illustrate the effect of comparatively large self-induction (elec- 
tro-magnetic inertia) in prolonging the oscillations in electric circuits, 
a series of photographs of an oscillating circuit having a very long 
period was taken by means of an oscillagraph at the Pender Electrical 
Laboratory, University College, London. In a circuit having a 
capacity of 7 mf,, an inductance of 31.5 millihenrys, and a resistance 
of 7 ohms, 2.5 complete oscillations were photographed. By keeping 
the self-induction and resistance constant and decreasing the capacity 
gradually to 0.5 mf . the number of complete oscillations increased to 
8. If the capacity had remained constant and the self-induction 
had be<»n increased, the same result would have been noted, i 

To illustrate the dampening effect of resistance, the capaciw and 
inductance which gave 8 complete oscillations was kept constant and 
the resistance of 7 ohms increased: 23 ohms gave but 6 complete 
oscillations; 59 ohms gave but 4 complete oscillations. 

This shows that receiving circuits of high resistance may have no 
pronounced period. 

176. Where it is required to greatly increase the wave length of an 
aerial in order to receive from stations using a much longer wave than 
that of the receiving station, it is necessary to insert a loading coil (in 
the shape of a variable inductance) in the aerial, unless a large capacity 
in series with the aerial is already installed. As this is not usually 
the case, it follows that the only means of lengthening the aerial is 
by adding inductance; but since this can be added at a different 
point from the inductance necessary for transferring energy to the 
closed circuit, the latter can remain fixed. (See fig. 40a.) 

From the foregoing considerations it appears that, generally speak- 
ing, we have fixed capacities and variable inductances in sending cir- 
cuits, and variable capacities and fixed inductances in receiving cir- 
cuits, and where variable inductance is necessary in a receiving 
circuit it can be added in a special cOil without affecting the mutual 
induction between circuits. 

Wliere receiving circuits have high resistance it is found by experi- 
ence, as was predicted by Prof. G.W.Pierce, that while it is necessary 
to adjust the open circuit of the receiver to the incoming waves, the 


closed circuit, after a definite relation of its capacity and inductance 
has been obtained, need not be adjusted further, because no increase 
of its natural period given by adding capacity will increase the 
strength of signals, no matter how much the open circuit is increased, 
^^y decrease of capacity below the critical amount, however, rapidly 
decreases the strength of signals. 

Doxrrz WAVE meter and its use. 

177. Fig. 53 is an illustrative diagram of a Donitz wave meter and 
PI. XIV a photograph of the instnmient. 

It consists of a standard closed oscillating circuit containing a fixed 
inductance and variable condenser inductively connected to a small 
closed circuit containing a coil of fine platinum wire in series. This 
wire is in the bulb of an air thermometer. If the standard oscillating 
circuit is placed near another oscillating circuit (such as the open or 
closed sending circuit) , so that the lines of force cut its plane, oscillat- 
ing currents will be induced in it. The currents in the standard cir- 
cuit induce other currents in the circuit containing the platinum wire, 
which becomes heated and heats the air in the thermometer. The air 
expands and elevates a column of liquid to a point which can be read 
on the thermometer scale. 

By movement of the variable condenser plates, the capacity, and 
therefore the wave length, of the standard circuit can be varied at 
will, the pointer on the condenser moving over a scale graduated 
directly in wave lengths. 

When the standard circuit is in resonance with the circuit whose 
wave length it is desired to ascertain, the current in the standard is 
a maximum as is also the induced current in the circuit containing 
the platinum wire, and consequently the heating effect on the plat- 
inum is a maximum. This is indicated by a maximum reading of 
the thermometer. 

Three fixed inductances are furnished with this wave meter, called 
by its inventor an ondameter, and there are three scales, one for each 
coil in combination with the condenser. The condenser is made 
up of 24 movable metal plates and 25 fixed metal plates immersed 
in paraffin oil. The instrument has an ebonite top and base and 
glass sides. 

178. The fixed inductances furnished with the instrument , are for 
a range of wave lengths from about 45 to 1,200 meters: 

Coil I inductance =0.0028 millihenry or 2.8 microheniys. 

Coil II inductance= .021 millihenry or 12.1 microhenrys. 

Coil III inductance= .05 millihenry or 50 microhenrys. 

The least capacity of the variable condcn.«cr is 0.000179 mf. 

The gi^atest capacity of the variable condenser is 0.00779 mf. 

With coil No. I wave lengths up to approximately 300 meters can be measured. 

With coil No. II wave lengths up to approximately 600 meters can be measured. 

With coil No. Ill wave lengths up to approximately 1,200 meters can be measured. 


It will be noted that each inductance is approximately four times 
as large as the next lower. 

The wave length can be calculated from the formula: Wave length 
in metal's = 1,884.95 \^ CL where C is in microfarads and L is in 
microhenrys, the formula being derived from the fundamental one 
T=27C\/LC where Tis the time of complete oscillation. 

179. Connections for measuring the wave length of the open, 
closed, and coupled circuits are sho\^Ti in I, II, III, upper left-hand 
comer, fig. 54. 

When the wave length of the closed or exciting circuit (II) is 
being measured, the open circuit is disconnected and the closed cir- 
cuit excited with sufficient energy to give a clear, bright spark of 
moderate length. 

The capacity of the closed circuit is such that a relatively large 
amount of energy is contained in it. 

Tlie large, oscillating currents produce correspondingly strong 
magnetic fields, so that good readings on the thermometer can be 
obtained without difficulty when the wave meter is one or more feet 
distant from the helix. The plane of the wave-meter coil must, of 
course, be parallel to the plane of the helix. 

Aerials for wave lengths up to 425 meters have very small capaci- 
ties as compared with those in the closed circuit, so that the mag- 
netic field is weak and good readings more diffii'ult to obtain. On 
this account a special coil of one turn is furnished with the instru- 
ment for insertion inside the wave-meter inductance in series with 
the aerial. The inductance of this turn is so small that its effect 
in increasing the wave length of the aerial is negligible. 

In measuring the natural wave length of the aerial (I) the latter 
is disconnected from the closed circuit and a spark gap inserted in 
series between it and the ground. A sufficient number of turns of 
the common helix in direct-connected sets, or of the aerial helix in 
inductively connected sets, is added to give it the period desired 
after its natural period has been obtained. 

A maximum reading of the thermometer shows the position of 
resonance and corresponding wave length. Other readings, when 
plotted (Curves I and II, fig. 54) with corresponding pointer read- 
ings, as abscissae and thermometer readings and as ordinate^, give a 
number of points which may be joined by a curv^e. The latter indi- 
cates by its shape the sharpness of resonance and in a general way the 
distribution of energy. 

After the range of wave lengths it is possible to obtain in the 
closed and open circuits is ascertained (fig. 55) and the shape of the 
waves determined (Curves I and II, fig. 54), the circuits are coupled 
together, the shape and length of the two waves sent out plotted 
(Curve III, fig. 54), and the percentage of coupling obtained. The 


percentage of coupling on all Slaby-Arco sets varied between 10 and 
15 per cent. 

Fig. 56 shows a combination of curves like those in figs. 54 and 55. 
It represents the original installation on the West Virginui^ with a 
very close coupling, nearly 40 per cent. 

Fig. 57 shows the original installation on the Marylandy and is an 
example of very loose coupling, there being but one wave length 
found. Excellent results with this set have been obtained. 

Fig. 58 shows the original and present installations on the Charles- 
touy which show two maxima — one 12 per cent and the other 7 per 
cent coupling. Figs. 58a and 58b those on the Indiana and Minne- 

Figs. 59 and 59a show the installation at the Guantanamo station; 
coupling, approximately 38 per cent. 

The method of tuning receiving circuits, by using the wave meter 
as a sender, has already been described. 

Fig. 61 shows a tuning curve of a Slaby-Arco syntonizing coil with 
an aerial of 325 meters. 

Fig. 62, that of a Shoemaker coil at the Jupiter Inlet station. 

180. Were it not for the fact that the values of the capacity and 
inductance in an aerial can not usually be determined prior to its erec- 
tion, standard lengths of connecting wdres used in installing wireless 
telegraph sets could be adopted, and the entire range of sending and 
receiving wave lengths and the correct coupling of any wireless tele- 
graph set might be determined beforehand. It is to be hoped that 
this will yet be done. 


180a. The hot-wire ammeter furnished for tuning the open and 
closed circuits to resonance is probably a more sensitive indicator for 
use in the wave meter than the air thermometer furnished and is fre- 
quently used in place of the latter. 

A hot-wire ammeter is shown on PI. XV, with shunts for use with it 
secured on the under side of the cover, m the upper portion of the 
figiu'e. It is for use in the open circuit. 

When the currents in the aerial are large enough to throw the 
pointer oflF the scale, one of the shunts should be connected in parallel 
with it. 

The hot-wire ammeter, as its name indicates, measures compara- 
tively the amount of heat generated in the aerial. The heat in any 
circuit in which a current is flowing equals P J?, or the product of the 
square of the current and the resistance. 

A high, as compared with a low, reading of the hot vdve ammeter 
shows that more energy is being dissipated in the o^pen circuit, but it 
does not show whether it is going out in persistent or highly damped 


oscillations, nor whether the coupling is tight or loose. Since the dis- 
tribution, as well as the total amount of energy radiated, affects recep- 
tion, the hot-wire ammeter is useful only to indicate resonance. For 
any coupling or wave length a maximum reading will be obtained 
when the two circuits are in resonance, but this maximum will be dif- 
ferent for different percentages of coupling. 

It is foimd that when two circuits tuned to resonance are coupled 
together, that the radiation, as shown by the hot-wire ammeter, varies 
somewhat with the coupling and is in general greater with a coupling 
of 15 per cent or more, than with a very loose couphng. 

The coupling that gave the highest reading of the hot-wire ammeter 
was usually found the best when receiving with coherer detectors, but 
since the introduction of detectors requiring the use of telephone 
receivers the tendency is toward very loose coupling, which shows but 
one maximum and gives out more persistent wave trains, i. e., with less 
damping. However, as previously stated, receiving circuits with the 
same natural wave length and coupling as the senders should work 
efficiently on either tight or loose coupling, and there is not sufficient 
data yet available to determine wWch is the best. 

The close coupling shown in figs. o9a and 60 is partly due to the 
necessity of adding inductance to the aerial at those stations to bring 
it into resonance with the closed circuit. 



181. In any case the open and closed circuits should be in reso- 
nance. This is of the greatest importance. 

The removal of a jar from the condenser on account of piercing, 
blistering of the tin foil, bad connections to tin foil, moisture in jar 
rack, change of helix connections, each and all change the wave length 
of the closed circuit and throw it out of resonance with the opeji cir- 
cuit, with marked decrease in sending qualities. 

In the same way, change in the amount or arrangement of wire, or 
lead of the aerial, changes its hatural wave length and has the effect of 
putting the two circuits out of resonance. 

When a wave meter is not part of the station equipment the hot- 
wire ammeter test should be made daily. In makuig the test care 
should be taken to have the length of spark gap and strength of current 
used always the same. The cause of any decrease in maximum read- 
ing of the hot-wire ammeter should be sought for first in the condenser 
and its connections, then in the condition of the spark gap, and finally 
at the ground and other connections of both circuits. 

It is found that the capacity of bare-wire aerials varies very little 
with widely varying atmospheric conditions, so that, generally speak- 
ing, the causes of decreased radiation are found in the closed circuit 


and nearly always in the change of capacity in the condenser, due to 
broken or poor contacts, blistering, dead foil, etc. 


182. This type of wave meter is shown in fig. 63. PL XVT is a 
photograph of the complete instrument. 

It consists of a sliding tubular condenser formed of two brass tubes, 
separated by an ebonite tube which forms the dielectric. 

The outer tube can be moved by a handle A, and an index pointer P 
(fig. 62) moves with it over a divided scale S S. 

Parallel with the condenser is an inductance coil II II, consisting of 
a bare copper wire wound on an ebonite tube. 

From the outer end of the condenser O, a pin 1 projects, which car- 
ries a half collar K, resting on the inductance coil. 

The circuit of the condenser and inductance (forming a standard 
oscillating circuit) is completed by a copper bar Lj Lg of square sec- 

With the instrument is supplied a vacuum tube ^V," which is 
attached to two small hooks placed on the ends of copper wires, which 
are respectively connected with the outer and inner tube of the con- 

These instruments are made in different sizes for measuring wave 
lengths up to 2,500 meters. Those for measuring wave lengths up to 
700 meters have the following constants: 

Wave length 100 meters: Inductance, 24.9 itiicrohenrys; capacity, 
0.000119 mf. 

Wave length 700 meters: Inductance, 162.3 microhenrys; capacity, 
0.000771 mf. 

183. To measure the period #f any circuit, place the cymometer 
so that the copper bar L^ Lg is parallel wnth, and close to, any straight 
portion of the circuit in which electric oscillations are taking place. 

Fix the vacuum tube to the two small hooks in connection" with 
the terminals x and y and screw the ebonite handle into the thick 
collar Ic of the outer tube of the sliding condenser. 

Move the handle, thus sliding the outer tube of the condenser 
along, until the vacuum tube glows most brightly. Then the end 
of the index slip P will indicate on the lowest of the four scales the 
number of oscillations in one-millionth of a second. 

The top scale reading indicates the oscillation constant of the cir- 
cuit being tested, viz, the square root of the product of the capacity 
in microfarads and inductance in centimeters of the circuit. 

The other two scales give the wave length of the circuit in feet and 
meters, respectively. 

It is generalty necessary when using this instrument to connect to 
the earth the terminal of the vacuum tube which is in connection 


with the outer tube of the sHdino: condenser. The copper bar Lj I^ 
should be placed as far from the circuit to be tested as it is possible to 
obtain a glow in the vacuum tubes. Such a position vn\l give a very 
sharp scale reading. 

Two kinds of vacuum tubes are furnished with the instrument, 
viz, neon and carbon dioxide tubes. The former is more sensitive 
and its excitation is more easily distinguishable in daylight. 

184. The cymometer differs from the Donitz wave meter in having 
a variable instead of a fixed inductance. The inductance and capac- 
ity are varied simultaneously by the movement of the outer con- 
denser tube, since it carries the pointer and the contact maker on the 
inductance. It will be noted that the inductance changes one turn 
at a time. 

The wave form, as determined by the heat in the air thermometer, 
can not be plotted with the cymometer, there being no scale reading 
for the vacuimi tube and no method of recording its relative bright- 
ness. The cymometer does, however, show the length of the two 
waves sent out. 

For measuring small mductances and capacities a rectangular cir- 
cuit of insulated wire, having an inductance of 5,000 centimeters, is 
furnished with the cymometer. B3' placing this inductance, whose 
capacity is too small to be considered, in circuit with an unknown 
capacity and measuring the wave length of the circuit thus found, 
the value of the capacity can be determined from the oscillation 

By connecting it with a known capacity and an unknown induct- 
ance and measuring the wave length of the circuit thus formed, the 
value of the imknown iiiductance can be determined in the same 


185. The wave meters first used were the Slaby measuring rods, 
a diagram of which is shown in fig. 64 and a photograph in PL XVII. 

A set for measuring wave lengtlis up to 1,200 meters consists of 
tlu'ee rods, the smallest, measuring wave lengths from 100 to 200 
meters, the intermediate, from 200 to 500 meters, and the largest, 
from 500 to 1,200 meters. 

Each rod consists of a glass tube closely covered with a winding of 
fine, silk-covered wire, forming an open circuit of large inductance. 

Inside the glass, at the upper end of the tube, is secured a fluores- 
cent screen, consisting of a small piece of paper covered with conduct- 
ing particles (preferably gold foil) and crystals of barium platina 

This screen is attached to the upper end of the wire. The lower 
end of the wire is brought up inside the glass and ends near the fluo- 


rescent screen described above. A metal plate, to be laid on the 
(ground and connected by means of a wire with a metal contact rod, 
is furnished with the instrument. 

\Mien brought near a circuit in which electrical oscillations are 
taking place, the induced potential at the ends of the wire will cause 
the screen to fluoresce, if the two circuits are in resonance. By mov- 
ing the contact maker along the coil its effective length is changed. 
The wave length corresponding to any point of contact is marked 
directly in meters on the coil. When in resonance the wave length 
Ls read from the scale at the point of contact which gives the brightest 

The three forms of wave meters described and the hot-wire ammeter 
are available for tuning sending circuits. The Donitz wave meter is 
the only one with which receiving circuits can be tuned. 


186. Closed receiving circuits having fixed inductances and variable 
condensers, or vice versa, can be provided with a scale on the variable 
element graduated directly in wave lengths, and by their means the 
wave length of any station heard can be measured by adjusting until' 
a maximum of sound is obtained and then taking the scale reading 
of the variable element. 

Receiving circuits having both variable condensers and induct- 
■ ances should be provided with a table showing the wave lengths for 
a number of adjustments of each variable. 


187. The importance of careful tuning can not be overestimated. 
Where a number of vessels and shore stations must be mutually 

ready to hear each other's calls at any time, thej- must necessarily 
call in the same tune, and each ship and shore station must keep its 
receiving circuits adjusted to that tune* 

By careful adjustment with the Fessenden interference preventer, 
it is possible to receive at will one of two incoming signals of the 
same strength and to exclude the other when the wave lengths differ 
hy 3 per cent, but if the signals which it is desired to exclude are much 
stronger, on account of proceeding from a near-b}^ station or from any 
other cause, this percentage of difference must be much greater, and if 
very strong it may not be possible to exclude the stronger and receive 
the weaker signals. 

It is necessary to call in a particular tune; it is not, however, neces- 
sary to communicate in that tune. 

The selection of the tune for the communication should be made by 
the receiving station when it acknowledges the call. 


There is a limit in this respect, however, since the range of wave 
lengths which can be effectively used with any given aerial is miu li 
more restricted in sending than in receiving. 

Increasing the sending wave length by adding inductance beyond 
that necessary- to receive energy from the closed circuit, rapidly 
decreases the sending range. 

When inductance is added to increase the receiving wave length, no 
evil effects result, at least, not to such a great extent. 

The above may l)e expressed by sa^'ing that a station can not send 
effectively on a wave more than 25 per cent longer than the natural 
wave length of its aerial, but it can effectively receive (by adding 
inductance to the aerial or by shortening it by means of a capacity in 
series) waves of almost any length. 

It is very desirable for the purpose of communicating between shore 
stations that sending wave lengtlis be used which are longer than those 
that can be efficiently used at ship stations. 

If a shore station aerial can not send out a ship^s wave length and 
vice versa, it will be necessary to have two receivers at each station, 
one kept in tune for each of the two wave lengths. This is done at 
high-power stations, separate aerials being installed for receiving from 

It will be seen from the above that the problem of assigning non- 
interfering tunes to a large number of intercommunicating stations is 
by no means a simple one, especially when the stations, such as ships, 
are continually varying their distance from each other. It has not 
yet been successfully solved. 

This problem will be greatly simplified as soon as means for sending 
and receiving in any desired direction only are perfected. 


188. A more serious cause of interference, however, especially at 
stations in warm climates, is what is commonly called ''static." 

Every lightning discharge produces powerful electric waves which 
affect detectors at great distances, and since thunderstorms in warm 
climates, and especialty in the summer, are sometimes almost continu- 
ous in the sense of existing somewhere in the area in which waves 
created by the lightning discharges affect detectors, the interference 
caused by tliem is also almost continuous. 

These waves vary greatly in length. Those of the same or nearly 
the same length, as any given aerial, affect that aerial more or less 
strongly. Those widely different are excluded unless very strong. 

Again, at every station the air at the top and foot of any aerial is 
at different potentials. The atmospheric potential gradient at any 
station varies with the time of day, the season of the year, and the 
local weather conditions. It is usuall}^ steeper in summer. 


This diflFerence of potential tends to equalize itself through the aerial. 
The upper air is usually positively electrified, the earth negatively. 
The amoupt and regularity of the discharge to ground at any time 
depends on the .difference of potential between the upper air and the 
ground at the time and the amount of electrified air which comes in 
contact with the aerial. 

The discharges are usually intermittent and vary in strength; some- 
times they are almost continuous and are described "as a continuous 
roar, through which it is impossible to read signals. 

In this respect the note of the spark (the frequency of the wave 
trains) affects reception, a high, clear note being easier to read than 
any other. Less sensitive detectors can sometimes be successfully 
used when static disturbances render the more sensitive ones useless. 

^Tiatever tends to selectivity or inertia in receiving circuits, such 
as Targe inductances, also tends to decrease static interference. 

It is found that closed receiving circuits not directly connected to. 
the open circuit are less affected b}' static. 

The static charges, having a direct path to ground, do not accumu- 
late on the aerial, and the aerial being only inductively connected to 
the closed circuit, impulses out of tune are much weakened in the 

When the signals it is desired to read are strong, static can be largely 
eliminated by disconnecting the ground without destroying the signal. 


189. Fig. 65 is a complete diagram of connections of a Slaby-Arco 
wireless-telegraph set supplied with current from a mercury-turbine 

Figs. 66, 67, 68, 69, 70, and 71 are diagrams of connections of com- 
])lete wireless telegraph sets furnished by Massie, Fessenden, Tele- 
fimken, Stone, Shoemaker, and De Forest, respectively. All of these 
sets are designed to use 60-cycle alternating current instead of inter- 
nipted direct current, as used in the Slaby-Arco sets. 

On board ship, motor generators are installed in the dynamo room or 
operating room or outside the latter in its immediate vicinity for trans- 
forming the ship's direct current into 110-volt A. C. The A. C. gen- 
erator leads are connected with the primar}' of an induction coil or 
transformer, the secondary of which delivers it at a potential of 25,000 
to 30,000 volts to the sending condenser. 

Figs. 72, 73, 74, 75, 76, and 77 are diagrams shovy^ing the standard 
methods of installation, control, and protection adopted. 

190. Sending sets work most efficiently when the interruptions or 
alternations of cuiTent are in resonance with the circuit formed by the 
secondary of the transformer and the sending coudenser. 


111 order to provide for some variations in the resonant frequency 
due to change of capacity in the sending condenser, the speed of the 
motor generator is made variable, so as to give any frequency bet\veen 
50 and 70 cycles. 

As previously stated, 60 cycles, normal frequency, are used because 
this is a commercial type of motor generator. It appears probable 
that a higher frequency will give better results. 

The reading of the frequency indicator when supplied with such sets 
should be frequently noted while sending and the speed maintained, by 
adjustment of the motor field rheostat, at the exact frequency shown 
by experience to be the best. 

When running on open circuit practically no work is being done by 
the motor except that necessary to overcome friction. 

When the primary circuit is closed by the sending key, with the 
spark gap opened, so that no sparking takes place, the secondary of the 
transformer charges the condenser during the first half of each alterna- 
tion and receives current from the condenser during the second half of 
each alternation. 

The load thrown on the motor generator by pressing the key depends 
on the period in a cycle at which contact is made, but, generally speak- 
ing, it may be considered as instantaneous ^^fuU load." 

If the spark gap is set so that the condenser potential breaks it down, 
the oscillations of the closed sending circuit practically cut out the 
secondary of the transformer, so that a condition of instantaneous 'no 
load " exists as soon as the spark passes. As soon as these oscillations 
cease the secondaiy again begins to charge the condenser and a condi- 
tion of almost instantaneous full load is established. This interval is 
so short that the inertia of the moving parts of the motor generator 
prevent any change of speed or voltage, so that the instantaneous full 
load thrown on when the key is closed is the one affecting operation. 
Again, the inertia of the moving parts of the motor generator is often 
sufficient to keep up the voltage during the length of a dot, but not 
during the length of a dasli. 

^Vhen the key is closed the momentary current starting at that 
instant depends only on the reactance of the primary of the trans- 
former and of the generator armature, since the resistance is ver}' low. 

To control this sudden rush of current an adjustable choke coil, 
called a reactance regulator, is placed in the primary circuit. This 
coil, on accoimt of its inertia, acts as a dead resistance or buffer against 
sadden changes of current, and by means of its adjustability enables 
the phase relation of the E. M. F and current in the circuit to be varied 
and thus the power expended to be controlled. (See par. 89.) 

Since the reactance regulator controls the power expended, it con- 
trols the secondary voltage and the maximum spark gap that can be 


By placing the sending key in shunt around it and having an indue- * 
tive resistance in series with the key the reactance regulator can be 
adjusted so that no sparking will take place, but by closing the key the 
current added through the shunt circuit is sufficient to cause sparking 
to take place. By means of this method (first introduced with the 
Shoemaker sets and shown in figs. 70 and 72, etc.) the sudden changes 
from full to no load are avoided and the regulation improved, and 
since oiily a small portion of the total sending current is broken at the^ 
sending key it is much easier to keep the contacts in good condition. 

On account of the small penetrating effect of high-frequency cur- 
rents (see par. 92) , it is believed that high voltages when associated with 
frequencies of above 100,000 per second are not dangerous to human 
life, but low frequency, high-voltage currents are verj^ dangerous, 
and it must be borne in mind that a condenser being charged and 
discharged at the alternator frequency is very much more dangerous 
than when it is discharging across the spark gap. 

For the above reason, a safety switch, shown in fig. 72, etc., is 
placed in the primary lead when the method of control d,escribed 
above is installed. 

This switch should only be closed when sending and should be 
opened at all other times when the motor-generator is running. The 
charge and discharge of the condenser when not sparking is indicated 
by a rustling sound, which signifies danger. 

This warning applies equally to induction coils and transformers, 
both terminals of which are dangerous when using alternating cur- 

Instructions for resuscitation from apparent death from electric 
sheet are given in Appendix F. 



191. Burnouts and damages to insulation from induced high poten- 
tials are referred to in paragraph 130. 

The protective devices shown in fig. 74 may consist of Leyden jars 
or other condensers, straight filament lamps, micrometer spark jjhps, 
or any other form of liigh noninductire resistance. 

At shore stations wires leading from power house to oj)erating 
room should be lead covered or nin in conduit, the covering^ to be 
grounded in all cases, the object being to afford a straight path to 
ground for all high potentials, and at the same time avoid current 

Carbon resistance rods, being a commercial article and not easily 
destroyed, are generally used for this purpose. 



192. Any dot and dash code may be used for signaling. For official 
use between ships of the Navy and between them and naval shore 
wireless-telegraph stations, the Continental Morse Code has been 
adopted. Instructions governing its use are issued by the Bureau of 
Navigation in the pamphlet '^Instructions for the Transmission of 
Messages by Wireless Telegraphy,'' which is supplied to all operatoe>. 
The pamphlet also contains the names of all naval ship and shore 
wireless telegraph stations and their **call letters.'' Information to 
the public relating to naval shore stations is issued in "Notices to 
Mariners." The rules governing communication between shore sta- 
tions and private vessels are pyblished in the same manner. Tliese, 
together with the* 'Regulations for the Government of Shore Stations,"' 
will be found in Appendices G, H, and I. 

Communication with private shore stations and coasting vessels in 
the United States is by means of the American Morse code; with all 
foreign stations, ship and shore, public and private, by means of the 
Continental Morse Code. It is probable that the call for the Inter- 
national Code of Signals, P. R. B., will soon be adopted by maritime 
nations for use in wireless telegraphy, so that, by means of the Inter- 
national Signal Book, communication can be carried on between opera- 
tors not speaking the same language. At the same time the use of the 
International ^Signal of Distress, N. C, should be extended to wireless 

The Continental and American Morse codes and a list of common 
abbreviations follow : 

A dash is represented as equal in length to tlu-Qp dots. • 

The interval between two elements of a letter is equal in length to a 
dot. , . 

The interval between letters in a word is equal in length to a dash. 

The interv al between words in a sentence is equal in length to two 

Telegraph codes. 




American Moree. 

Continental Morse. 

A '.... 


m a ■ 

m aa^B m m 


m^^ . ■■■. m 





H '. 


J : 





. . 

— ^ 



«^ aa^B . ^t^m 





m m t^^m 










l>on't undemtand 


Finish . 





'(/*t/i^^/>r*^ ^— -^ • . 




Telegraph codes — Continued. 








Fraction line 



Pound sterling 

Capitalized letter 

Colon followed by quotation 

Dollar mark 

Decimal point 



Underline (begin) fc. , 

Underline (end) 

Parenthesis (begin) 

Parenthesis (end) , 

Quotation marks (begin) . , , 

Quotation marks (end) , 

Quotation within a quotation (begin) . . . 

Quotation within a quotation (end) 


Spell 'dot" 

Abt About 

Af After 

Agn Again 

Amn American 

Amt Amount 

Anr Another 

Ar Answer 

Ar\" Arrive 

Atk Attack 

Atl Atlantic 

Awa Away 

Awi Awhile 

Ax Ask 

Ay Any 

B* Be' 

Bal Balance 

Bd Board 

Bid Bundle 

Bf Before 

Bg Being 

, Bn Been 

Bot Bought 


Jin uae in United States telegraph services.] 

Bro Brother 

Bk Break or back 

Bt But 

Btn Between 

Btr Better 

Bu Bushel 

Byd Beyond 

Bz Business 

Bat Battery 

Bbl Barrel 

C See 

Ca Came 

Cg Seeing 

Chg Chai^ge 

Or Care 

Ct Conntict 

ay City 

Cvl Civil 

Cx Capital letter 

Col Collect 

Ck Check 

Da Day 






Did Delivered 

Dr Doctor 

Drk Dark 

Dux Duplex 

DH Deadhead 

Ea Each 

Ed Editor 

Eng Engine 

Etc Etcetera 

Ev Ever 

Evn Even 

Exa Extra 

Fl Feel 

Fid Field 

Fig Feeling 

Flo Flow 

Fit Felt 

Fm From 

Fri Friday 

Frt Freight 

Gr Ground 

G. B. A . . .Give better address 

G.A Go ahead 

G. S. A . . .Give some address 

G. M Good morning 

G. E "Good evening 

G. X Good night 

Gen General 

Gpf German 

Gg Going 

Gu Guard 

Gv Give 

Gvg Giving 

Hb Has been 

Hhd Hogsboad 

Hid Held 

Him Helm 

Hm Him 

Hnd Hundt«d 

Hon.-. Honorable 

Hpn Happen 

Hqrs Headquarters 

Hr Here 

Hs His 

Hu House 

Hv Have 

Hw How 

Ify Infantry 

W Import 

L^ It is 

I Ixu It is understood 

I Kp Keep 

! Kpg Keeping 

; Kpt Kept 

{ Kw Know 

Kwg Knowing 

Kws Knows 

Las Last 

Lat Latitude 


Lit Little 

Lk Like 

Lt Lieutenant 

Lv Leave 

Lvg Leaving 

Lvs Leaves 

Lyg Lying 

Ma May 

Mab Maybe 

Maj Major 

Mar March 

Mas Master 

Mat Material 

Max Maximum 

Mch Machine 

Mcy Machinery 

Md Made 

Mem Member 

Mfd Manufactured 

Mgr Manager 

Mil Much 

Mil Military 

Min Minute 

Mk Make 

Mkg Making 

Mkr Maker 

Mks Makes 

Mkt Market 

Ml Mail 

Mng Morning 

Mny Many 

Mo Month 

Mon Money 

MH Marshal 

Msg Message 

Msk Mistake 

Mst Must 

Mv Move 

Myn. v.. -.Million 

Na Name 

Xd Need 

Nee Necessary 




Neg Negative 

Ni Night 

No No, and New Orleans 

Nun None 

Nv Never 

Nw Now 

Nx Next 

N. M No more 

Ofc Officer 

Ofr Offer 

Ofs Office 

Opr Operator 

Ot Out 

Otr Other 

Ov Over 

O. K AU right 

Pc Percent 

Pd Paid 

Ph Perhaps 

Pha Philadelphia 

Pm Postmaster 

Po Post-office 

Pod Post-Office Department 

Pot President of the 

PotuH President of the United States 

Pr. President 

Pra. Pray 

Prt Part 

Pt Present 

Qk Quick 

Qnig Quartennaater-Gt»neral 

Qr Quarter 

R Are 

Re Receive 

Red Received 

Reg Receiving 

Rcr Receiver 

Res Receives 

Ret Receipt 

Rek Wreck 

Rht Right 

Rlf Relief 

Rp Report 

Rpt Repeat 

Rr Railroad 

Ru Are you 

Ruf Rough 

Ry Railway 

Sa Senate •^ 

Scottis Supremo 

Sd Should 

Court of the United 

Sdn Sudden 

Sec Section 

Sed Said 

Seni Seem 

Sen Seen 

Sh Such 

Shf Sheriff 

Shi .'.Shall 

Sig Signature 

Sik Sick 

Sis Sister 

Slf Self 

Slo Slow 

Sir Sailor 

Sni Some 

Sma Small 

Sn Soon 

Snc Since 

Snd Send 

Snr Sooner 

Snt Sent 

Sor Soldier 

Sp Ship 

Spfy Specify 

Spl Special 

Spo Suppose 

Ss Steamship 

St Street 

Sta State 

Stn Station 

Sto Store 

Str Steamer 

Sud Surround 

Sv Seven 

Svc Service 

Svd Served 

Sve Serve 

Svg Serving 

Svl Several 

Swo Swore 

Sx Dollar mark 

Sy Say 

S. Y. S See your service 

T The 

Tan Than 

Tg Thing 

Tgh Telegraph 

Tgm Telegram 

Tgr Together 

Tg\' Telegraphy 

Th Those 

Thk Thank 




Tho Though 

Thr Their 

Ti Time 

Tk Take 

Tkg Taking 

Tb Taken 

Tkt Ticket 

m Talk 

Tm Them 

Tn Then 

Tnd Thousand 

Tni To-night 

Tnk Think 

Tr There 

Tm Through 

Ts This 

Tae These 

Tt That 

Ttt That the (5) 

Tuf Tough 

Tw To-morrow 

Ty They 

U You 

^c You see 

Un Until 

Uni United 

Upn Upon 

Ur Your 

Vrg Uige 

Val Value 

Vy Very 

W With 

Wa Way 

Wat Water 

Wd Would 

Wea Weather 

Wg Wrong 

Wh.. Which 

Wi Will 

Wit Witness 

Wl Well 

Wlk Walk 

Wn When 

Wnt Want 

Wo Who 

Worn Whom 

Wos Whose 

Wr Were 

Ws Was 

Wt What 

Wu Western Union 

Wy Why 

Y Year 

Ya Yesterday 

4 Please start me, or where 

5 Have you anything for me 

9 Important official message 

13 Understand 

25 1 am busy now 

30 No more 

73 Accept best regards 

77 Message for you / 

92 Deliver 

"Wire'* — Give instant possession of line 

for test. 


193. For installation ample room is available at all shore stations. 

On board ship a room, having about 60 square feet of floor space, 
with no dimension less than 5 feet, should be provided for the installa- 
tion and operation of a wireless-telegraph set. The operating room 
should be well ventilated and lighted, as nearly sound proof as prac- 
ticable, and free from vibration. The exact location of the room is 
not of great importance, provided a good lead to it for the aerial can be 
obtained. The farther this lead is from large conducting bodies the 
better. Operating rooms below the water line, where long leads to 
aerial are necessary, are decidedly less efficient than those on the 
upper deck. 

The room should have a well-insulated entrance for the aerial and 
should be fitted with an operating table about 2^ feet wide, not less than 
7 feet long, and of convenient height for working the sending key 
while sitting down. 


The table should be strongly built of dry, well-seasoned wood. 

The instruments should be mounted on the table so that they are at 
safe sparking distance from each other and from any part of the oper- 
ating room. 

The receiving instruments should be as far away from the sending 
instruments as practicable. The induction coil or transformer may 
be mounted on the bulkhead or under the table. In any case it should 
be where its terminals are not likely to be touched accidentally. The 
motor generator is preferably installed near the operating room, but 
outside of it. It may be installed in the operating room or in the 
dynamo room. 

The connections between all parts of the sending and receiving 
instruments should be as direct as possible and in the case of the send- 
ing instruments they should be of large surface and well insulated by 
air or other nonconductors. Sharp turns in connecting wires should 
be avoided on account of brush discharges, which always start at cor- 
ners. The effect is the same as if the electricity were traveling too 
fast to turn corners. 

The necessity for bringing a number of leads to the combination 
switch for sending or receiving detracts considerably from the sim- 
plicity of the installation and to a slight extent from the efficiency of 
the set as a whole. 

High-potential leads should be kept well away from low-potential 
leads and where they cross it should be nearly at right angles. 

The ground connections should be electrically good and of large area. 
The diagrams of connections and the purpose and use of each connec- 
tion should be familiar to every operator. They should be well made 
and kept clean all the time. 

194. Wireless-telegraph instruments, like all others, depend for 
their efficiency on their condition and amply repay good care. 

Sending-key contacts should be kept clean and smooth and with 
faces parallel to each other. 

All sliding contacts, especially in receiver tunmg coils, should bo 
clean and bright and free from foreign matter. 

Detector points should be kept in their most sensitive condition and 
frequently tested by means of the buzzer furnished for the purpose. 

The best adjustment for receiving different stations should be 
recorded or memorized by all operators. 

A sending set worked at low power, with all connections good, closed 
and open circuits in resonance, no sparking from edges of condenser, 
jars, or plates, nor glow from aerial and no sparking to rigging, is utiliz- 
ing its power much more efficiently and will probably be heard farther 
than the same set puslied to the limit, but out of resonance or ^'ith 
liigh-reslstance comiections and sparking at all points. 


In any case use only current and gap necessary for good readable 
signals when sending to stations at known distances. 

Tuning curves for open and closed circuits are only correct for the 
capacity and inductance in each at the time the measurements are 
taken, and the radiation shown on the hot-ware ammeter after coupling 
the two circuits is that for the particular period and coupling, as well 
as for the primary current, frequency, and spark gap then used. 

These conditions should be reproduced as nearly as possible and the 
hot-wire ammeter test made daily. The cause of decreased radiation 
should be searched for imtil it is found and then remedied. The con- 
densers should be carefully examined weekly, as well as all contacts on 
all circuits, special attention being given to the ground connection. 

The insulation resistance of the aerial should be tested monthly or 
more frequently when leaks are suspected, and all insulation aloft 
should be frequently examined. 

Porcelain or glass insulators are preferred. Hard-rubber insulators 
char on the surface from leaks in wet weather and become less effective 
as insulators. 

Except where a number of tunes are ordered to be used the opera- 
tors should not alter the capacity nor inductance in either circuit, 
except when absolutely necessary, and when, wliile sending, any part of 
the condenser is injured it should be immediately replaced or repaired, 
and if this can not be done on account of lack of spare parts the two 
cu"cuits should be readjusted to resonance with the best means 

Operators must avoid a short or jerky style of sending. Dots and 
dashes must be firm and of proper relative lengths, as must also the 
interval between parts of a letter and the spaces between letters and 
words. The spark must be kept white and crackling and have con- 
siderable volume. 

PI. XVIII is a photograph of the Maryland's operating room. 

PI. XIX, operating room at Cape Elizabeth, Me, 

PI. XX, operating room at Portsmouth, N. H. 

PI. XXI is a photograph of the Colon station, exterior. 

196. The limits of the book will not permit giving detailed descrip- 
tions of methods of operating engines and dynamos at shore stations. 
Instructions for assembling, charging, and discharging storage bat- 
teries are given in Appendix K, and fig. 80- is a diagram of connections 
for the purpose. 

At all stations, ship and shore, the best results are invariably 
obtained and the most satisfactory service given by alert and careful 
operators who take pride in the condition of their instruments. 


Note 1. 

The following list of metals are arranged in such order that any one will be the positive 
pole of the battery when used with the metal next below it on the list as a battery elemfot 
and the negative pole when used with the element next above it, the difference of poten- 
tial between any two being greater the farther apart they are in the series. 

Carbon. Copper. Zinc. 

Platinum. Iron. ^>(agnesium. 

Gold. Tin. Sodium. 

Silver. Leao. 

The amount of potential difference also depends on the battery solution, and in some 
instances it may be reversed. 

Note 2. 

The relations existing between electricity and matter have been m(^ exhaustively inves- 
tigated by Prof. J. J. Thomson, who has proved that electricity has an atomic structure and 
that it can exist separately from an atom of matter. 

When a current is sent through a vacuum tube, the luminous beam proceeding from the 
cathode has In^en shown to consist of particles projected from the cathode. These particles 
are capable of turning a small wheel. The cathode beam can l)e deflected by either a mag- 
netic or ah electric field, and it is found to consist of particles of itegative electricity or of parts 
of the atom negatively charged, each having about one one-thousandth of the mass of an 
atom of hydrogen. 

These particles are the same, no matter what gas is used in the vacuum tube. They are 
usually called eUdrons. When an electron is broken off from an atom, the remaining part 
ih positively charged. Currents of electricity, however produced, are the result of the decora- 
IX)sition of atoms into positive and negative electric charges. There can be no electric cur- 
current without movement of electrons. Conductors are l)odies in which the breaking up 
of atoms and movements of electrons takes place more or less easily. Some free electrons 
exist in all bodies. It is by setting these into vibration and by means of this vibration mak- 
ing them break off similar particles from neighboring atoms, and thus propagate the dis- 
turbance throughout the ma^ss of the conductor that electric currents are generated. 



Appendix A. 

[Extract from Fleming's Cantor lecture, Journal of Society of Arts, p. 106, January 5, 1906. Taken 
mostly from A. Heydweiller, " On Spark Potential?." Ann. der Physik, vol. 248, p. 23.") (1898).] 

Spark voUage betu^een brass halls 2 ceniimeiers in diameter for various spark lengths. 

Spark length (In cms.) . ; ^f*/^ I Spark length (cms.) . vofta"^. 

0.1 , 4,700 !j 1 31,300 

n.2 8,100 ' 1.5 40.300 

fU 11,400 ,j 2 j 47,400 

0.4 14,500 I 2.5 1 53,000 

"^^ j 17,500 I 3 \ 57,500 

ae I 20,400 3.5 i 61,100 

0.7 23,250 1 1 4 .* ,....1 64,200 

0.8 26,100 4.5 67,200 

0.9 28,800 I 5 69,800- 

Appendix B. 

The *' flat-top" aerials now used to the exclusion of the "cage" type of the earlier outfits 
are made of two constructions — "single ended" and "double ended" — the single ended 
being of the inverted L formation, the double ended being of the T formation. There is 
also a minor variation applying to either, in which the outer ends of the "horizontal" 
cooductors of the aerial, which might for ordinary purposes be left open, are connected 
together, as later described in detail, so as to form an inverted U of the Hertzian "loop," 
which is required by the type of receiver circuits used by the De Forest and Shoemaker 

The single conductor from the transmitter runs to one terminal of the anchor spark gap 
furnished with the outfit of these companies, or to an alternative constmction shown on 
print No. 14831-A attached. 

The two legs of the inverted " U ' of the aerial attaching to the other two terminals. 

The first installation of the flat top double end aerial was made on the U. S. S. Kertiu^ky 
in 1904. 


The first standard wave length was 320 meters. This has since been superseded by 425 
meters for ship installations 

There an^ other longer wave lengths used in some special cases for shore stations. 

In every case it is highly desirable that the length and disposition of the aerial should be 
such that its natural wave length be that of the standard wave length. This has been found 
nece.«ary on account of the waste of energy in transmitting, due to the coils of inductance 
which are inserted to make up for inadequate length. 

The dimensions required m the aerial to give a natural wave length of 425 meters varies 
with the nature and relative location of the adjacent masts, smokestacks, etc., which will 
affect the values of its inductance and capacity and no exact fonnula can be assigned. 

The length of aerial required for 425 meters natural wave length will, however, in most 
cases, necessitate the use of the single ended form. 

The length of aerial (measured from the outer end of the "horizontal ' down through the 
"vertical" to the transmitter) giving the nearest practicable wave length to 425 meters, for 
four wire aerials was 219 feet in the case of the Minneapolis where the natural wave length 
was 406 meters for a double end flat top aerial. For a single end flat top aerial, a length 
of 275 feet measured similarly, gave a natural wave length of 403 meters on the U. S. S. 


In the cases of ships where these lengths are not practicable, it may be necessary to increase 
the inductance of the aerial by reducing the number of wires from the st-andard number of 
four for a part of the length of the aerial. 


Examples of aerials installed are shown on blueprints attached as follows: 

U. S. S. New Jersey and Rhode Idandy single-ended loop, drawing No. 15301-M. 

U. S. S. Minneapolis J double-ended loop, drawing No. 15377-M. 


The spars forming the aerial are of two lengths, 15J feet, which have been used on ships of 
the Denver class and larger, and 10) feet, 'which have been used on ships smaller than those. 

The 15J-foot spars are 3J inches in diameter in the center and IJ inches diameter at the 
ends; the lOJ-foot spars are 2 J inches diameter in the center and li inches diameter at 
the ends. 

In the case of double-ended aerials metal spars have been used for the center spar, to 
avoid the possible damage to wood from the heat from the stacks. These have the following 

For the larger aerials 15^ feet length, IJ inches outside diameter, and for the smaller 
aerials 10) feet lengths, 1) inches outside diameter, No. 17 B. & S. gauge. 


Tlie insulators used in connection with the installation are as shown on blueprints 9244-H 
and 9899-C and others as specially described in the following: 

The uses of those shown on 9244-H are as follows: 

The deck-tube insulator 9244-11-4 is used for going through bulkheads and decks in loca- 
tions whore water-tightness is not specially required, but there are liabihties to mechanical 

In going through metal decks and bulkheads, it is customary to increase the distance 
between the conductor and the metal by the use of a deck-tube plate 9244-H-21. 

The window tube 9244-H-6 is not ordinarily used. It includes a detachable part which 
enables the aerial to be disconnected from the apparatus in the case of lightning storms, and 
be connected direct to ground, thus protecting the apparatus and operator. 

The strain insulator 9244-H-20 has ordinarily been used for the ends of the aerial and to 
secure the halyards which hoist the aerial into place. 

The strain clamp and insulator 9244-H-23 is used at the lower part of the aerial and 
attached usually a}x>ut 3 feet from the upper end of the rat-tail, and from there guys to 
another adjacent part of the ship, keeping the aerial in stretch. 

The suspending insulator 9244-H-24 is used in guys which supplement the strain clamp 
and insulator. 

Capping 9244-H-25 and molding 9244-11-26 are in some cases run in quarters where it 
is desired to protect the rat-tails from mechanical injury, and also, to some extent, persons 
from shock. 

The deck tube, protected, type A, 9899-(\ has been superseded by an improved modifi- 
cation shown as type B on the same sheet. 

This type of insulator is used on decks where the moisture on the deck from washing 
down, storms, etc., and the mechanical contact with holystones and other objects is to be 

The suspending insulator has been largely superseded by the use of the Locke strain insu- 
lator No. 605, especially adapted as sliown on print 13993-A and photograph 1644. 

Its first application was made on the U. S. S. Charleston. 

These insulators remove the objection encountered with the use of rubber insulators, i.e., 
carlx>nization from sparks, consequent leakage of aerial, and give in their petticoats two dry 
surfaces of porcelain for efiFective insulation in rainy weather. 


The special form of insulator shown on print 15367-A was used on the IndiaTia for run- 
ning the rat-tails along the passage to the operating room. 

Id the particular construction shown, rubber insulators of similar dimensions were used as 
an expedient, porcelain insulators from the Pass & Seymour Co. not being available at the 

In drawing 9244-H-30 is shown the rat-tail angle block. 

This is used in connection with the rat-tails where guys are taken off, in order to prevent 
too sudden a nip in the rat-tail. 

In the strain insulator and strain clamp and insulator a porcelain insulator Xo. 20, as 
shown, is used in connection with the seven No. 20 phosphor-bronze conductor at the wooden 
and biaus spars on the aerials, as will be explained later. 

The porcelain tubes which are used in the aerial insulators, drawing 15367-A, are known 
as ''porcelain tubes, glazed, heads 3 inches long, 1-inch hole, 1} inches outside diameter, 6 
inches under head" for rat-tail, and are made by Pass & Seymour, Incorporated, Dey street, 
Xew York. 

The aerials are swung from a band with eyes, which are fitted on topgallant mast under 
tmck lights in compliance with the Bureau of Equipment's letter of February 20, 1905. 

The runs of the lower part of the aerial to the operating room are either through decks, 
masts, or ventilators, as the case may require. 

The conditions depend upon the protection ^rom mechanical injury which is required, an 
important feature being the maintenance of as large as possible distance from the rat-tails to 
the metal part of the ship. 

In the case of masts and ventilators, the distance to metal may be as great as 2 or more 
feet, as compared with 6 inches, which is obtained With the use of the protected deck tube, 
type B, 9899-C. 

Total weights are about 325 pounds. 


The aerial to be flat-top single-ended, of- /Ten/ucty type (12802-L), modified for the Hertz 
C'loop") circuit, so as to be adapted for the Shoemaker receiver installed. 


The aerial will be swung between the fore and main topgallant masts. 
Just below the bottom of the truck lights there will be installed a band with eye and two 
lignum-vitfe, yacht blocks, No. 9, for the halyards. 


Two spruce yards, 15 feet 6 inches long, 3 inches diameter in center, and 1 J inches diameter 
at ends, to be of clear timber, without knots or checks, and coated with three ci.dts of 
spar varnish. 

The yards to be located 161 feet apart. 


Four Locke strain insulators, No. 605 (12086-X),with ash plugs as per 13993-A, to Ix? 
lashed with 10 turns of marline to the inner sides of the wooden yards at 2 feet from ends 
(as per No. 1686, etc.), and arranged to set vertically when the aerial is in place. 

Notch the yards, if required, to fit the bead on the No. 605 insulators. 

The ash plugs to be given three coats of spar varnish and fitt^^d with four 3-foot bridles 
of 18-thread hemp rope, with one-half inch thimbles. The thimbles will be so located tliat 
the No. 605 insulators will set vertically when the aerial is swung into place. The bridles 
and UDglazed surfaces of the No. 605 insulators to be given two coats of Armalac. 



On the after yard will be secured, at 59 inches ai>art, four sets of (2 to set) 7/No. 20 phos- 
phor-bronze wire leads, each 1 foot long, at the 8 ends of which will be No. 20 porcelain 
insulators, 2 inches diameter, five-eighths inch groove, three-eighths inch hole (requisition 
No. 1014/05) for insulation from the yard. 

Of each set of two, one is to extend on the forward side "horizontally'' and one "down." 

From the insulators on the four horizontal leads to the forward yard four 160-foot "hori- 
zontal" wires will be secured to the other groove of each "horizontal" No. 20 insulator. 

Also, from the after-yard four "vertical'' wires 7/No. 20 phosphor-bronze, 85 feet long, 
to extend from the lower four No. 20 porcelain insulators to the rat-tails. 

The breaks in the open angles will be closed by a bight of 7/No. 20 phosphor-^bronze wire 
soldered to the " horizontal '' and " verticals, '' with no tension and slightly slack, when aenal 
is in place, the eight 1-foot leads taking all the strains. 

At the forward yard the four wires will be joined together by soldering a cross wire of 
7/No. 20 phosphor bronze, without interfering with the Locke insulators, 1 foot from the 
wood yards. 

The leads and wires to be spaced 59 inches apart on all yards. 

The sag allowed in center yard is 3 feet from the level of the blocks, or 102 feet to the 
superstructure deck. 

Of the four vertical wires 85 feet long, the two on the starboard side will lead to a rat-tail 
and the other two on the port side to a second rat- tail. 

The stranded conductors in the rat-tails at the upper ends will be thoroughly filled with 
splicing compound, so as to prevent moisture which runs down the "verticals" from enter- 
ing inside of the rubber of the rat-tail. 


In splicing the 7/No. 20 phosphor-bronze wire to make up the necessary lengths use 
Mclntyre twist connections (requisition No. 324). 

Where practicable the runs of the 7/No. 20 P. B. wire shall be unbroken and from the 
same lot of wire. 


To two awning stanchions, outboard, starboard, and port, at frame 73 on the after bridge 
deck secure two guys of paraffined signal halyard stuff, one at either side to strain clamp 
and insulator 9244-H-23, which are clamped to the rat-tails at about 3 feet from the upper 
ends of the rat-tail. 


Two leads 35 feet long, to be run separately tlirough two "long. head" glazed, porcelain 
tubes, head 3 inches long, 1-inch hole, 1 J inches diameter outside, 6 inches long under head, 
or, if not available, rubber, substitutes 15367-A, cemented into deck tube plates 9244-H-21. 

Thes<> plates will be softened in hot water and bent to conform to curve of the outside of 
the mast at 10 feet above the bridge deck. 

A similar pair of plates will be fitted to the mast under the superstructure deck, and also 
to the forward bulkhead of operating room frame 76-77. 

In the mast, at distances of 4 feet apart, will l)e placed five pine sticks 4 by 4 inches by 4 
feet long secured to 1} by li-inch angle-iron brackets at each end. 

In these sticks will Ik* drilled at the center two IJ inch holes 6 inches c. c, for the porce- 
lain tubes or their nibber substitutes. 

The rat-tails will Ix' run from their junction with the "verticals" through these insulators 
to a lightning switch, type B, 14898- A, to be located overhead in the operating room. 

Midway l)etween the mast and the operating room install an aerial insulator 15367-A, to 
support the runs of rat-tail. 




From the thimbles in the bridles of the wooden yards, through the blocks secured to the 
bands on the fore and main topgallant masts, halyards of 21-thread manila rope will be 
rove and secured to cleats, to be located on the inside of the lower military tops. 


From the thimbles in each bridle a guy of 9-thread manila rope will be run to a second 
thimble at the upper rigging band of topmast, for the purpose of keeping the wooden yards 
squared up. 


In two locations 2 feet apart above the connection to the rat-tail fasten a weather drip of 
marline to carry off all rain or condensed moisture before it reaches the rat^tail and allow a 
slight sag to the rat-tails for the same purpose before they enter the mast. 


On the after side of the mast below the deck plate on the superstructure deck secure a 
danger name plate 15372 — A. 

Make up complete and furnish all appliances as mentioned above for installation excepting 
blocks, guys, halyards and cleats. 

Spares to hefyrnished. — One No. 605 Locke strain insulator without plug, 200 feet 7/No. 
20 phosphor bronze wire, feet 19/No. 25 rat-tail conductor. 

Acc488ones to he furnished. — Lightning switch, type B, 14898 — A ; print of aerial. 


As made: 
160 feet horizontal. 
85 feet vertical. 
35 feet rat-tail. 

280 feet total. 

- - r^ 


^ As fitted in place: 

feet horizontal/ / 
■ feet ¥ eitital r<^^'' 
-^-^ feet rat-tail to switch. 

feet switch to antennte helix. 

feet ammeter to jar case. 

feet total. 


Designed for use on wave length, 425 meters. Natural wave length as installed, 

meters. Inductance inserted to increase wave length to 425 meters, turns on antennae . 

inductance. Length on forward end reduced feet to reduce the natural wave length to 

425 meters. 

For adjustment data see cur^'e No. . 


The conductors used for aerials are shown on print 15418 — A, the 7/No. 20 phosphor 
bronze wire being used for the " horizontal " and *' vertical" parts of the aerial, 19/No. 23 
phosphor bronze " rat-tail " wire being used for the lower parts of the aerial where run through 
decks, mast^s, ventilators, bulkheads, etc., and of the parts above deck or outside of masts 
where a person is liable to come in contact with and receive a shock from the aerial. 

The No. 26 B. & S. tinned iron wire is not used in connection with aerials, but for serving 
night-signal cables, truck lights, and rigging, where aerials are installed in compliance with 
Bureau of Equipment's letter of February' 20, 1905. 


The McLityre connectors are used for making splices where necessary to secure the 
required length in the phosphor bronze and 19 No. 23 rat-tail conductors. 

The object of these connectors is to prevent the softening and weakening of the hard 
drawn wire in soldering as far as may be practicable. 

It is customary to paraffin a length of about 10 feet of the upper part of the halyards and 
an equivalent amount of the signal halyard guys in order to assist in reducing leakage in 
damp weather. 


In order to give the necessary warning as to possible danger from contact with the rat-tail 
conductors, it is desirable to install a danger name plate in their immediate vicinity, as 
shown on print 15372 — A. 


A convenient form of switch for grounding the aerial when not in use or in the case of 
excessive static charges is shown in print 14898 — A, attached. . 

These are secured to the deck above in the operating room, which grounds the two lugs 
direct in the case of a metal deck. 

If the deck is of wood it will be necessary to lead off a strip of copper to ground. 

The two legs of the aerial making the loop connect* to the short back ends of the switch 

The leads to the receiver connect to the two lower switch contacts. 

The aerial from the transmitter connects to the center contact on the crossbar. 

The two spark gaps form the equivalent of the " anchor spark gap " used by the Shoe- 
maker and De Forest outfits. 

To insure exact similarity in spark length in each side of the loop the gaps should be 
adjusted by using a piece of ordinary postal card as a gauge. 


In tuning aerials a desirable form of record for the readings is E. O., Form No. 291 ; the 
readings being later plotted in curves similar to those shown on prints 14826 — A, U. S. S. 
Marylarui; 1537r>-A, U. S. S. Minneapolis: 14825— A, U. S. S. Weal Virginia; 1544a-A. 
V.S.S. Charleston. 

In measuring natural wave length of aerials some difficulty is ordinarily encountered from 
arching instead of an oscillatory spark across the gap in obtaining a sufficient indication on 
the thermometer of the hot-wire ammeter of the Donitz wave meter. 

A convenient method of obtaining the dCvsirable character of spark is by the use of the 
spark gap for exciting aerials, as shown on print 15368 — A. 

This is niserted between the single-turn coil of the Donitz Tvave meter and the aerial. 

The other end of the single-tuni coil is connected to the ground. 

The high-tension terminals of the induction coil connect direct to either side of the spark 

Appendix C. 

Wireless-telegraph specification No. 13936- A. 



[E, O. No. 1287.] 

No. 107688 1 Bureau of Equipment, 

SSR. ALC. I Washington, D. C, February go J906. 

Sir: In order to provide suitable elevation for and to minimize induction between aerial 
conductors for wireless telegraphy and the rigging and other conductors, the following gen- 
eral instructions will be observed: 

1. All battle ships, armored cruisers, and other cmisers of and above 4,000 tons displace- 
ment should have masts measuring not less than 130 feet from truck to water line. 


2. On vessels of and above 2,000 tons but less than 4,000 tons mastheads should not be 
Ifss than 120 feet and in gunboats and monitors not less than 100 feet from truck to water 

3. AD topmasts and topgallant masts should be of wood. 

4. A light band with an eye on forward and after side should be fitted imder each truck, 
to which a block may be attached for hoisting the aerial conductor. 

5. Topgallant rigging to be of hemp. 

6. Topmast rigging should be of wire, set up with hemp lanyards or approved strain insu- 
ktors. and if more than 50 feet in length should be served for a distance of 10 feet near the 
middle of the length with waterproof insulated soft-iron wire. No. 26 B. & S. 

7. Lifts and braces of signal yard. — ^Lifta should be made of wire. Braces should be made 
of wire, with hemp tails on whips below tops of smokestacks. Where braces are within 15 
feet of and parallel or nearly parallel to the aerial conductor, they shall be served near the 
middle of the length with insulated soft-iron wire, as above. 

8. Lo^eer rigging. — If the aerial conductor passes parallel or nearly parallel to and within 
15 feet of the lower rigging, the lower end of the rigging will, if set up with turn-buckles, 
be served for 10 feet with insulated iron wire as above. 

. 9. Jacobus ladder. — If made of wire, will have short hemp pendants or strain insulators at 
the bottom. 

10. Ladder of night signal set. — Will have short hemp pendants or strain insulators at the 

11. Lightning coriductor. — To be fitted with lightning conductor break, type A, No. 10218, 
at the lower end. The upper section should pass within one-half inch of the metal of the 
ship if possible. 

12. Truck light conductors. — To have the equivalent of 6 turns 10 inches in diameter in 
the lower part of the upper section, (these turns to be taken around the topmast if con- 
venient), or to be sensed for 10 feet with insulated iron wire about 50 feet from the truck. 

13. Night signal set conductors. — To be wrapped for 10 feet with insulated iron wjre. No. 
26 B. <fe S., about 50 feet from the upper light where most convenient. 

14. Where hemp lanyards are used there will be at least 2 feet between dead-eyes when 
set up. 

lo. These instructions supersede those already given for vessels now building where the 
rigging has not already been purchased by the contractor. 
Very respectfully, 

H. N. Manney, 
Chief of Bureau of Equipment. 
The Coiof AKDANT, Navy-Yabd, New York. 

Appendix D. 

The relay requires frequent adjustment; it should be tested every morning to see if it is 
sufficiently sensitive. It should ring readily through 20,000 ohms external resistance on a 
single-oeU circuit, but should not be oversensitive; that is, it must open the local-battery 
circuit shaiply and without chattering when its own circuit is broken. The local-battery 
contacts in relay and the weak- battery contacts on tongue of decoherer must be kept clean 
<uid in good condition. The contacts on coherer and on multiple switch must also be kept 

The decoherer must give a sharp, decisive blow against the coherer; care must be taken 
that this blow is not strong enough to break the coherer. The w^eak-current contact on 
tongue should break just before this blow is delivered. A little practice enables the oper- 
ator to judge when the decoherer is in proper adjustment, and once this is obtained the jam 


nuts should be screwed down on adjustment scrpvra and the decoherer should remain in 
adjustment. The same remarks apply to tlie Morse writer, where the adjustments are still 
more numerous. This writer worHs in parallel on the same circuit as the interrupter. Its 
armature must be somewhat sluggish, since it is required to stay down on an interrupted 
current while the interrupter makes a series of blows for a dash, and it roust rise sharply 
at end of dots and dashes. 

The Morse writer is a clockwork mechanism driven by means of a spring and fitted with 
an automatic release and stopping device. It contains in all six adjustments, viz., adjust- 
able counter spring, against pull of magnets, top and bottom contacts for adjusting position 
and movement of armature, adjustable counterbalance of armature, adjustment of lift 
of printing disk, of point of release of mechanism, and of speed of tape. The normal speed 
of tape is about 3 feet per minute, and adjustment is effected by altering the tension of spring 
on fan governor. The downward movement of armature releases driving mechanism and 
hfts printing disk against tape, so that these two functions must be considered in adjusting 
limits of armature movement. The speed of movement of annature,and hence the sharp- 
ness of the record on tape, is controlled by downward pull of magnets, upward pull of counter 
spring, and position of counterbalance. The magnet pull on armature is increased by 
diminishing distance of armature from core and by strengthening battery. As only four 
cells, 6 volts, are wanted on decoherer, however, and the two have to work in parallel, it is 
not feasible to change battery strength. The counter spring lifts armature back, after the 
current is broken in magnet coil, against the pull from residual magnetism and friction. 
The armature and counterweight should be in equilibrium on point of support of connecting 
arm, so that counter spring has no weight to lift. 

Faulty working and record may be caused by - 

1. Failure of releasing mechanism to release. 

2. Insufficient lift of writing disk. 

3. Insufficient drop of writing disk. 

4. Too weak downward pull of magnets. 

5. Too weak upward pull of spring. 

6. Failure of clockwork to feed tape. 

7. Failure of automatic stopping device to act. 

1. Take off cover of clockwork and press armature down (take brake off governor) if 
releasing mechanism is O. K. A little pawl will be lifted out of spring catch by armaturr^- 
rod extension and drawn back by small spiral spring. This movement will turn a cam 
and release mechanism. If by downward movement of armature the pawl is not lifted 
out of catch, increase downward movement of armature slightly. If still not released, 
lower position of catch by means of the adjusting screw until it will release when arma- 
ture is pressed down. 

2. When not in raised position the writing disk should turn freely with its lower third 
in the ink well and with the upper edge about 2 millimeters from tape; when raised it 
should press firmly against the tape. If in normal p»?sition disk is fully 2 millimeters 
from tape and when raised does not press finnly on tape, lower position of armature 
slightly: if not sufficient, raise disk slightly by means of the adjusting screw on armature 
from extension on inside of box. (This adjustment affects the automatic starting dence, 
which may have to he readjusted.) The disk should make a smooth continuous line on 
tape as long as the armature is held down and cease working promptly when the armature 
is released. 

3. If the normal position of disk is too close to tape, dirt in ink or a mechanical jar 
may make mark on tape when armature is not depressed. The limited movement of 
disk may also prevent sufficient movement of armature to release starting device. The 
adjustment is made in the inverse sense of No. 2. 

4. Test the battery and see that it is up to voltage — 5.5 to 6 volts. Slack off on counter- 
spring. Move normal position of armature closer to magnet core by screwing down on 
upper stop. See that armature beam is not jammed in its mountings. 


5. Increase tension of spring. Raise lower armature stop so as to lift armature slightly 
from inagnet core. A slip of paper over ends of core so as to prevent armature from 
coming in actual contact with core will frequently improve the working. 

6. If the mechanism runs freely with tape out there is too much tenision on tape. If 
the mechanism is released and wound up and will not run there is too much friction in 
i^me of its bearings or gear, and they must be gone over, cleaned, and oiled. The 
trouble will usually be in some relatively high-speed bearing or gear. If with tape in the 
inochaniam runs but does not feed tape the pressure of rollers on tape must be increased. 

7. This is usually due to some overadjustment under heading No. 1 and must be cor- 
Tided in the inverse sense. It may, however, be caused by spring on catch or cam pawl 
being too weak or by dirt or excessive friction in cam pawl. If the cam pawl does not 
fly forward to front position in seat when released by cam the trouble is in it or its spring. 
One complete revolution of tape pulley is made after last downward movement of arma- 
ture before automatic stop acts. 

Appbndbx E. 

1. Tte headgear will consist of two watch-case telephone receivers, mounted by univer- 
sal joints on adjustable covered strap, and arranged so as to be conveniently held on the 
head of the operator. 

2. Hie receivers are to have a powerful permanent magnet and to be wound with silk 
or enamel covered copper wire of diameter over copper not less than 0.0015 inch. Dia- 
phragm to measure 1} inches by 0.004 inch. The last few turns on the coils will be of 
heavier silk-covered copper wire. All joints to be rosin soldered. The resistance of each 
receiver will be between 1,000 and 1,100 ohms. 

3. The two receivers will be connected in series with a flexible cord giving a free length 
of at least 4 feet. The cord will consist of two rubber-insulated conductors, with pin 
terminals at both ends. The conductors will have seven straqds of No. 32 B. & 8. copper 
wire or the equivalent. The cord from each telephone will be joined 15 inches from the 
receivers and continued for 4 feet 6 inches. Joints to be neatly made. No'part of the cord 
to have more than two conductors. The conductors will be covered and held together with 
a p;reen silk braid. 

4. Strap will be of nickel-plated steel, covered with a thin coating of black hard rubber. 

5. Each receiver will be fitted with pneumatic ear cushions of approved typo. 

6. Weight of set not to exceed 15 ounces. 

7. Each set will be supplied with one extra cord, complete. 

8. Each telephone will be tested for receiving qualities and must give results equal to 
standard sample. 

Appendix F. 

[By -Vugustln H. Goelet, M. D.] 

The urgent necessity for prompt and persistent efforts at resuscitation of victims of acci- 
dental shocks by electricity is very well emphasized by the successful results in the instances 
recorded. In order that the task may not be undertaken in a half-hearted manner, it must 
be appreciat«d that accidental shocks seldom result in absolute death unless the victim is 
I<*ft unaided too long, or efforts at resuscitation are stopped too early. 

In the majority of instances the shock is only sufficient to suspend animation temporarily, 
owing to the momentarj' and imperfect contact of the conductors, and also on account of the 
pp<istance of the body .submitted to the influence of the current. It must be appreciated also 
that the body under the conditions of accidental shocks seldom receives the full force of the 

2740—06 9 


current in the circuit, but only a shunt current, which may represent a very insignificant 
part of the whole. 

When an accident occurs, the following rules should be promptly executed with care and 
deliberation : 

1. Remove the body at once from the circuit by breaking contact with the conductors. 
This may be accomplished by using a dry stick of wood, which is a nonconductor, to roll the 
body over to one side, or to brush aside a wire, if that is conveying the current. When a 
stick is not at hand, any dry piece of clothing may be utilized to protect the hand in seizing 
the body of the victim, unless rubber gloves are convenient. If the body is in contact with 
the earth, the coat tails of the victim, or any loose or detached piece of clothing, may he 
seized with impunity to draw it away from the conductor. When this has been accom- 
plished observe rule 2. The object to be attained is to make the subject breathe, and if this 
can be accomplished and continued he can be saved. 

2. Turn the body upon the back, loosen the collar and clothing about the neck, roll up a 
coat and place it under the shoulders, so as to throw the head back, and then make efforts to 
establish respiration (in other words, make him breathe), just as would be done in case of 
drowning. To accomplish this, kneel at the subject's head, facing him as shown in fig. 1, 
and seizing both arms draw them forcibly to their full length over the head, so as to bring 
thorn almost together above it, and hold them there for two or three seconds only. (This is 
to expand the chest and favor the entrance of air into the lungs.) Then carry the arms down 
to the sides and front of the chest, firmly compressing the chest walls, and expel the air from 
the lungs, as shown in fig. 2. Repeat this maneuver at least sixteen times per minute. 
These efforts should be continued unremittingly for at least an hour, or until nutural respira- 
tion is established. 

3. At the same time that this is being done, some one should grasp the tongue of the sub- 
ject with a handkerchief or piece of cloth to prevent it slipping, and draw it forcibly out 
when the arms are extended above the head, and allow it t^ recede when the chest is com- 
pressed. This maneuver should likewise be repeated at least .sixteen times per minute. 
This serves the double purpose of freeing the throat so as to permit air to enter the lungs, 
and also, by exciting a reflex irritation from forcible contact of the under part of the tongue 
against the lower teeth, frequently stimulates an involuntary effort at respiration. To 
secure the tongue if the teeth are clenched, force the jaws apart with a stick, a piece of wood, 
or the handle of a pocketknife. 

4. The da^shing of cold water into the face will sometimes produce a gasp and start breath- 
ing, which should then be continued as directed above. • If this is not successful the spine may 
be rubbed vigorously with a piece of ice. Alternate applications of heat and cold over the 
region of the heart will accomplish the same object in some instances. It is both useless and 
unwise to attempt to administer stimulents to the victim in the usual manner by pouring it 
down his throat. 

While the above directions are being carried out, a physician should be summoned, who, 
upon his arrival, can best put into practice rules 5, 6, and 7, in addition to the foregoing, 
should it be necessary. 


5. Forcible stretching of the sphincter muscle controlling the lower bowel excites power- 
ful reflex irritation and stimulates a gasp (inspiration) frequently when other measures have 
failed. For this purpose, the subject should be turned on the side, the middle and index 
angers inserted into the rectum, and the muscle suddenly and forcibly drawn backward 
toward the spine. Or, if it is desirable to continue efforts at artificial respiration at the same 
<ime, the knees should be drawn up and the thumb inserted for the same purpose, the subject 
retaining the position on the back. 

6. Rhythmical traction of the tongue is sometimes effectual in establishing respiration 
when other measures have failed. The tongue is seized and drawn out quickly and forcibly 
to tl«i Jimit, then it is permitted to recede. This is to be repeated 16 times per minute- 


7. Oxygen gas, which may he readily obtained at a drug store in cities or large towns, is a 
powerful stimulant to the heart if it can be made to enter the lungs. A cone may be impro- 
viaed from a piece of stiff paper and attached to the tube leading from the tank, and placed 
over the mouth and noee while the gas is turned on during the efforts at artificial respiration. 

Appendix G. 


(Published by the Hydrographlc omce. Washington, D. C. Noveml^er 22, 1904. No. 47a.] 

The following regulations governing the use of the United States naval coastwise wireless 
telegraph stations are hereby established: 

1. The facilities of the naval coastwise wireless telegraph stations (including the one on 
the Nantucket Shoal light-ship), for communicating with ships at sea, where not in compe- 
tition with private wireless telegraph stations, are placed at the service of the public gener- 
ally and of maritime interests in particular under the rules established herein, which are 
subject to modification from time to time, for the purpose of — 

{a) Reporting vessels and intelligence received by wireless telegraphy with regard to 
maritime casualties, derelicts at sea, and overdue vessels. 

(6) Receiving wireless telegrams of a private or commercial nature from ships at sea, for 
further transmission by telegraph or telephone lines. 

(c) Transmitting wireless telegrams to ships at sea. 

2. For the present, this service will be rendered free. All messages will, however, be sub- 
ject to the tariffs of the ship stations and land lines. Arrangements have been made with 
both the Western Union and Postal Teleg^ph companies for forwarding messages received 
from ships at sea. When a message is not prepaid the company deliverin*; it will collect the 
charges. Shipowners should arrange with companies operating the land lines as to tariffs 
and the settlement therefor. Messages will not be accepted for transmission to ships whose 
owners have not agreed to accept unpaid messages, unless a sufficient sum is deposited to 
cover all charges. 

3. The Nantucket Shoal light-ship station will report vessels and transmit messages from 
them if the signals are made by the international code or any other known to the operators 
on the light-ship. 

4. When notified by the Weather Bureau of the Department of Agriculture, naval wire- 
less-telegraph stations will give storm warnings to vessels communicating with them by 
virelcfls telegraphy. Storm warnings wiU soon be sent to the Nantucket Shoal light-ship 
by wireless telegraphy and storm signals furnished by the Weather Bureau will be dis- 
played therefrom to warn passing vessels. 

o. All vessels having the use of the naval wireless telegraph service are requested to take daily 
meteorological observations of the weather when within communicating range and to trans- 
mit such observations to the Weather Bureau by wireless telegraphy at least once daily, and 
transmit observations oftener when there is a marked change in the barometer. 

6. Arrangements for a time^ignal service by wireless telegraphy are now being made. 

7. All shipowners desiring to use any special code of signals for communicating with the 
Xantucket Shoal light-ship station or any of the shore stations or make any other special 
arrangements are requested to communicate with the Bureau of Equipment, Navy Depart- 
ment, Washington, D. C. 

8. All chambers of commerce, maritime exchanges, newspapers, news agencies, and others 
desiring to have vessel reports and general marine news forwarded to them regularly are 
requested to conmiunicate with the Bureau of Equipment in order that necessary arrangt*- 
ments for the service may be made. In no case will an operator attached to a station be 
allowed to act as an agent for any individual or corporation, but all vessel reports and marine 



news not of a private nature will be supplied to all applicants, ao long as this senrioe does 
not too greatly tax the personnel of the stations, when it will be necessary for those desiring 
information involving much time for its distribution to appoint agents, who wiU be allowed 
access to the station bulletins. 

9. Naval wireless telegraph stations are equipped with apparatus of several systems and 
can communicate with all the principal wireless telegraph systems now in use, if tuned to 
the same wave length. The Department is desirous of cooperating with all shipowners 
wishing to avail themselves of its wireless tel^raph service, and, judging from its expe- 
rience with numerous systems, it is believed that there will be little or no difficulty in 
arranging for communication between its stations and ships equipped with apparat4is of 
other systems, if the owners of the apparatus as well as the owners of the ships are desirous 
of establishing such communication. 

10. Vessels desiring to make use of this service regularly must agree t-o transmit and 
receive all Giovemment messages free. 

The following stations are fully manned and will be prepared to receive messages at all 
hours, except in case of some accidental breakdown, which is not apt to occur because of 
the precautionary measures which have been taken. 

The call letter is given in the column opposite the name of each station: 


Call. J 
letter. I 


' ^?tter. 

Navy-yard, Portsmouth. N. H ' PC 

Cape Ann (Thatchers Island) PE 

Highland Light, Cape Cod .Mass | PH 

Nantucket Shoal light-ship PI 

Torpedo station. Newport, R.I PK 

Montauk Point, L.I PR 

Navy-yard, New York PT 

Highlands of Navcsink, N.J PV 

Cape Henry, Va I QN 

Navy-yard, Norfolk, Va '. . . .| QL 

Dry Tortugas, Fla I RF 

San Juan, P. R s A 

Culebra, West Indies I SD 

Yerba Buena Island, Cal ^J TI 

Navy-yard, Mare Island, Cal TG 


It is expected that the following stations will be in operation in a few weeks, fully manned 
to receive messages at all hours: 


I letter. 

Cape Elixabeth,Me ' PA 

Navy-yard, Boston, Mass PG 

Naval station, Key West, Fla | RD 

Navy-yard, Pensacola. Fla RK 

Naval station, Guantanamo, Cuba SI 


I letter. 

Panama Canal Zone 

Farallon Islands, Cal 

Naval station, Cavite, P. I . 
Cabra Island, P. I 



The following stations are equipped with apparatus but are not yet fully manned; they 
ill receive and transmit messages when operators are on duty: 



Naval Academy, Annapolis, Md ^. ' QG i Navy-yard . Washington, D. C QI 



The Bureau of Equipment expects to erect wireless telegraph stations at the principal 
points along the coast of the United States and at points in its insular possessions. As fast 
as they are completed they will be open for public use under the regulations established 

Notice will be given in the "Notices to Mariners" when stations are put in operation o^ 
withdrawn from the serv^ice for any reason. 


Messages for the Cape Ann station should be forwarded via the navy-yard, Portsmouth, 

The Nantucket Shoal lightship will transmit its messages to the torpedo station, New- 
port, R. L All messages intended to be sent by this light-ship to ships at sea should l)e sent 
to the toxpedo station. 

Messages for the Montauk Point wireless telegraph station will also be sent via the tor- 
pedo station, Newport, R. I. 

Arrangements have been made with the Weather Eureau for the transmission of messages 
between Cape Henry wireless telegraph station and Norfolk. All messages intended for 
the Cq)e Henry" station should be sent via the Weather Bureau, Norfolk, Va. 

All messages intended for Dry Tortugas should be sent via the naval station, Key West, 

The station at Yerba Buena, Cal., can be reached by either the Postal Telegraph or the 
Western Union system and the one at Mare Island by the W^estem Union. 

The Farallon station will conununicate with Yerba Buena Island, California. 


I. A vessel wishing to communicate with a station and having ascertained by "listening 
in" that she is not interfering with messages being exchanged within her range should make 
the call letter of the station at a distance not greater than 75 miles from it. 

II. The call should not be continuous, but should be at intervals of about three minutes 
in order to give the station a chance to answer. 

III. After the station answers the vessel should send her name, distance from station, 
weather, and number of words she wishes to send; then stop until the station makes O. K., 
signals the number of words she wishes to send to vessel, and signals go ahead. 

IV. Then the vessel begins to send her messages, stopping at the end of each 50 words 
and waiting until the station signals O. K. aqd go ahead; when all messages have been sent 
she will so indicate. If the sender desires to designate the Western Union or Postal Tele- 
graph 8y.stem for further transmission of his message, he should do so immediately after the 
address, as, for example: ''A. B. C, Washington, D. C, via W. U. (or P. T.)." 

V. When a vessel has indicated that she has finished, the station will send to the veas<'l 
such messages as she may have for her in the following order: 

(a) Government business, viz, telegrams from any Government Departments to their 
agents on board. 

(6) Business concerning the vessel with which communication has been established, viz, 
telegrams from owner to master. 

(c) Urgent private dispatches, limited. 

[d) Press dispatches. - 
(g) Other dispatches. 

yi. In the case of the Nantucket Shoal lightship, it will, immediately^ on receiving the 
vessel's call, acknowledge, and (after receiving vessel's name, distance, weather report, and 
number of words she wishas to send) transmit the first three to Newport, and then tell the 
vessel to go ahead with her messages. 

MI. After receiving these and sending the vessel any message on file for her, the light- 
ship will transmit to Newport messages received from the communicating vessel in the 
following order: 

(a) Government business. 

(h) Urgent private dispatches, limited. 

(c) Press dispatches. 

(i) Other dispatches. 

VIII. A naval wireless telegraph station has the right to break in on any message being 
sent by a vessel at any time, and the right of way may be given at any time to a govern- 
ment vessel or one in distress. 


IX. When two or more vessels desire to communicate with a naval wireless telegraph 
station at the same time, the one whose call is first received will have right of way, and the 
others will be told to wait and will be taken up in turn. Vessels having been told to wait 
must cease calling. 

.X. In case communication is hot established with any ship for which messages are on 
file, the naval wireless telegraph station will notify the telegraph company from which the 
messages were received, giving sufficient information for them to identify the telegrams 
and notify the sender. 

XL In order to obtain the best results, both sending and receiving apparatus should be 
timed to wave length of 320 meters. 

XII. Until further notice the speed of sending should not exceed 12 words per minute. 

XIII. In order that all messages received at naval wireless telegraph stations may be 
forwarded to ships for which they are intended, and in order that all ships equipped with 
wireless telegraph apparatus may receive storm warnings, they should always report when 
in signaling distance of a naval wireless telegraph station. 

XIV. The ser\'ice being without chaiige at present, the Government accepts no responsi- 
bility for the reception or transmission of messages from or for passing vessels. Every 
effort will be made to transmit all messages without error and as expeditiously as possible. 
It must be remembered thjit errors are not yncommon in ordinary telegraph and cable mes- 
sages, so that due allowance should be made. 

XV. In order that the ser\uce may be made as good and as useful as possible, it is requested 
that complaints should be promptly reported to the Bureau of Equipment as soon as possi- 
ble after the cause therefor, giving date, hour and other details, to enable the Bureau to 
investigate the case. 

XVI. Information regarding the naval wireless telegraph service will be published in 
" Notices to Mariners. ',' 

By order of the Bureau of Equipment: 

H. M. Hodges, 
Commander f U. S. iV., Hydrographer. 
Note. — Copies of these notices can be obtained by mariners, free of charge, by applying 
to the Hydrographic Office, to one of the branch offices, or to any of the agencies in sea- 
board or lake ports. They are also on file in all United States consulates, where every 
facility will be afforded for their inspection. Shipmasters are especially requested to inform 
the Hydrographic Office immediately of any newly discovered danger to navigation, or of 
the establishment or change of any aid to navigation. 

Appendix II. 

1. Tlie senior electrician will be held accountable for all Government property belonging 
to the station, and will receipt for all articles invoiced to him. llpon being relieved he will 
transfer the property to his successor, who will *«ign an itemized receipt for all supplies on 
hand in duplicate, one for each party to the transfer. 

2. There shall l)e kept a log Ixwk m which shall be recorded the temperature, the direc- 
tion and force of the wind, and the state of the weather and clouds, by symbols. Tlief* 
records shall l)e made every four hours during the time the operators are on watch, and if 
there are not enough operators at the station to permit of night watehes being kept, the 
maximum and minimum temperature during the night shall be recorded on the following 
morning. All meteorological phenomena, such as lightning, aurora borealis, fog, mist, 
snow, rain, etc., shall Im» remarked upon, together with a statement of the character of 
transmission of signals, if any are made during the period. If there are any atmoapbcHc 


signals during the period they shall be noted. Whenever atmospheric signals interfere 
with transmission, all the circumstances of atmosphere and weather shall be carefuUy 
noted. Tlie conditions of the weather which appear to be particularly advantageous and 
those which appear to be particularly disadvantageous for the transmission of signals shall 
be carefully obser\'ed and noted. Any regular recurrence of atmospheric signals shall be 
the subject of special report. The log book shall contain a list of stores expended, a record 
of the number of hours the engine or source of power supply is in use, of all accidents and 
repairs to any part of the apparatus, of the reporting and detachment of operatois, and 
other matters of interest. The log book shall contain a list of messages sent and received, 
the number of words and time of transmitting and receiving each message, the distance 
and wave length, and, for sending, the spark gap and power used for each message. 

3. The entries for the log shall be made by the operator on duty on a dail}^ log sheet pro- 
vided for the purpose. These shall be copied daily, in ink, in the log book, which shall be 
signed by the electrician in charge. 

4. The originals of all official messages sent and copies of all official messages received 
shall be carefully preserved and filed in a case provided for the purpose. These shall not 
be open for public inspection. 

5. There shall be kept in a book provided for the purpose an inventory of all Government 
property at the station. Upon being relieved the senior electrician shall inspect the sta- 
tion with his successor, and the latter shall acknowledge the receipt of the property over 
his signature in the inventory book, making a note of any exceptions as to items or their 
condition. The daily expenditure of supplies shall be kept in the log book, and a report 
of supplies on hand and expended made in the log book at the end of each quarter. 

6. All official messages received for further transmission shall be transmitted in the 
most expeditious manner by telegraph, telephone, wigwag, letter, or otherwise, depending 
on local conditions and circumstances, and a record of the time and method of further 
transmission made orf the original. All telegrams so sent shall be confirmed by mail to 
the same address as the telegram. 

7. A routine shall be made out which shaU provide for the efficient care and preservation 
of all parts of the station and apparatus, including protection from fire, the method and 
times of relieving operators, smoking regulations, and all other provisions necessary for 
the proper conduct of the station. A copy of this routine shaU be entered in the log book. 

8. There shall be no smoking in the vicinity of the gasoline engine or storage tanks for 
gasoline, nor in the vicinity of any house for the storage of oil. 

9. The arrangements for extinguishing fire shall be kept in readiness for instant use. 

10. The electrician in chaige shall keep a careful watch on all parts of the station and 
apparatus, such as condition of engine, mast and rigging, storage batt-erics, etc., and 
report at once by letter the need of any repairs 1 yond the facilities of the station. 

11. Requisitions for renewal of supplies shall be made not oftener than once a month, 
except in cases of emergency. 

12. All correspondence concerning the Bureau of Equipment shall be conducted through 
the commandant of the yard having control of the station. 

13. Electricians at stations on light-house reservations shall not interfere in any man- 
ner with the light keepers. 

14. The electrician in charge shall be subordinated to the principal light-house keeper 
in all matters' pertaining to the Light-House Establishment. 

15. Electricians at stations on light-ships shall be subordinate to the master of the 
light-ship in all matters pertaining to the Light-House Establishment and the discipline 
of the ship. 

16. A copy of these regulations shall he posted in each wireless telegraph station. 

H.N. ^Un ney , Ch ief of Bureau. 
NOVEICBER 15, 1904. 


Appendix I. 



A log book will he furnished by the Bureau of Equipment to all naval wireless-telegraph 
stations except those on vessels in oommission. 

The entries for the log shall be made by the operator on duty on a daily log sheet pro- 
vided for the purpose. Tlie log sheet shall be copied daily in ink in the log book, which 
shall be examined and signed by the electrician in charge. 

In the proper column there shall be entered for each message, in the order of sending 
and receiving, the number of words it contains, the time in minutes taken to sender 
receive, the distance of sedding or receiving station or vessel, if known, the wave length 
used in sending and receiving (except where standard wave length of station is used, when 
the letter "S" shall be entered), the spark length and power used in sending, and nnml)er 
of hours the source of power has been in use during the day. When the number of mes- 
sages sent or received is greater than the number provided for in the column, the record 
sliall be entered on the proper part of a daily log sheet and the same cut out and pasted 
in the smooth log book. The entries for the wind, weather, and clouds shall be by sym- 
bols in accordance with the forms printed herewith, and shall be made every four houre, 
as indicated in the columns, except when there are not enough operators at the station 
to pennit of night watches lx»ing kept, in which case the maximum and minimum tem- 
perature during the night shall be recorded on the following morning and the weather 
conditions at the time of record. The duration and relative intensity '(such as continu- 
. ous, irregular, intermittent, strong, weak, faint) of atmospheric signals shall be noted in 
the propter column, and the additional infonnation required by the Instructions for 
Wireless Telegraph Stations given under " Remarks. " The daily expenditure and n^ceipt of 
stores shall be entered, and these shall form the basis of the "Quarterly report, of stores.'* 
which shall accompany and form part of the log book. 

A statement shall be made daily in the proper column as to whether the station rou- 
tine has been carried out, and if not, in what n»spect and the reason therefor. 

Note in log book when stonn warnings are received from Weather Bureau and when 
sent out. 

Under "Remarks'' give names of all stations on vessels read or sent to during the day, 
with distance in sea miles, if known. 

Results of experiments of interest to be indicated by a star (♦) in upper right-hand 
comer of page, and if of unusual interest to Ix* reported immediately to the Bureau. 

On last page of " Remarks" give gi atcst distance of exchange of messages and greatest 
distance received caring quarter, with names of stations. 

Other entries shall be as indicated under their respective headings and as required by 
the Instructions for Wireless Telegraph Stations. 

The log book shall be forwarded quarterly to the Bureau of Equipment through the 


[statute miles per hour.] 

0. Calm 3 7. Fresh breezes 40 

\ 1 . Light airs 8 | 8. Moderate gales 48 

a,. Light breezes 13 9. Strong gales .% 

3. Gentle breezes 18 10. Gale 65 

4. Moderate breezes 23 , 11. Heavy gale 7.i 

5. Stiff breezes 28 12. Hurricane 90 and over. 

6. Fresh breezes 34 | 



4. Clear blue sky. 

c Cloudy weatlier. 

d. Drizzling or light rain. 

p. Passing showers or rain. 

q. Squally weather. 

r. Rainy weather or continuous rain. 

/. Fog or foggy weather. ! a. Snow, snowy weather, or snow falling. 

<7. Gloomy, or dark, stormy-looking , t. Thunder. 


A. llaU. 
/. Lightning. 
m. Misty weather. 
0. (h'ercast. 

u. Ugly appearance or thre>atening weather. 
V. Variable weather. 
w. Wet, or heavy dew. 
z. Hazy weather. 


Cimu {Ci.), — Isolated feathery clouds ol fine fibrous texture; "Mares tails." 

CirroSiraius (CiS.). — Fine whitish veil, giving a whitish appearance to the sky; often 
produces halos; "Cirrus haze." 

Oirro^umvlus (Oi-Cu.). — Small fleecy white balls and wisps, without shades, arranged in 
groups and often in lines: "Mackerel sky." 

AtUhCumuLus (A-Cu.). — Larger white or. grayish balls, with shaded portions, in flocks i)r 
rows, often so close that edges meet. 

AUoStratua {A. S.). — ^Thick veil of gray or bluish color, briUiant near sun or moon. May 
produce corons. 

StrojUhCumvlus (S-Cu.). — A suc43ession of rolls of dark cloud, which frequently cover tho 
whole 8ky. The characteristic cloud of storm areas, especially of the fore part of those areas. 

Xirnbug (*V.). — Rain cloud; a thick layer of dark clouds without shape, from which con- 
tinuous rain is falling. Ci-S. or A. S. is seen through the breaks. liow-lying fragments are 
known as "scud." 

Cumulus (Cu.). — Thick clouds whose summits are domes with protuberances, but whost* 
Iwses are flat. " Woolpack ' ' clouds. 

Vumtdo-Nim'bus {Cu-N.). — Thundershower clouds. Mountainous clouds surrounded at top 
by veil of false cirrus and below by nirabu.s-like masses of clouds. 

Stroiut (8.), — ^Horizontal sheet of lifted fog. 

Appendix K. 


[Normal charging and discharging rate, 20 amperes.] 


1. Great care should be taken in the unpacking and subsequent handling of the various 
pftrts of the battery, as many of them are easily broken or bent out of shape by roujjh 

2. Open the crates or packing boxes on the side marked " up " and carefully lift contents 
out. Never slide out by turning crate on its side. • 

3. Upon opening crates and boxes, carefully count the contents of each package and check 
vith the shipping list. A number of small parts will usually be found in each shipment , and 
^pp should be taken to examine packing materials to determine that no parts have \yvv\\ 

4. Immediately upon opening the crates the material should be carefully examined for 
Wkage. Cracked jars, whether of glass or nibber, should not be s<»t up, a.s if put into us<* 
^akage of acid may cause annoyance or trouble. 



5. The proper location of the battery is important. It should be in a separate room, which 
should be well ventilated, dry, and of moderate temperature. 

6. The temperature of the room should be between 50° and 80** F., normal being 70®. 
Extremes of temperature affect the proper working of a battery. The air should be dry, for 
if damp there is danger of leakage from grounds. 

7. The ventilation should be free, not only to insure dryness, but to prevent chanc«> of an 
explosion, as the gases given off during charge form an explosive mixture if confined. For 
this reason never bring an ejtposed jUime near the battery when it is gassing. 


8. Place the jars, after they have been cleaned, in position on the stands, which.should l)e 
provided for the purpose and which should be so situated in the room that each cell will b^ 
easily accessible. If the floor space is available, it is often preferable to install the colls on 
one tier, in which case the "stand " will be very much simplified, a set of stringers properly 
fastened together and the insulating bricks being all that is required. The jars are set in 
the trays, which should previously be filled even with the top with fine dry bar sand, tlie 
trays resting on the glass insulators. 

9. Place the elements as they come from the packing cases on a convenient stand or tabic 
(the elements are packed positive and negative plates together, the positives having plates 
of a brownish color, the negatives of a light gray. The negative always has one more plate 
than the positive), cut the strings that bind them together, and carefully pull the positive 
and negative groups apart, throwmg the packing aside. After carefully looking over both 
groups and removing any dirt, or foreign matter, place two hard-rubber separators on each 
pasitive plate about an inch from and parallel with each vertical edge and then slip these 
plates into position between the negatives, which have been placed crosswise on a board 
about two-thirds the width of the plates, so as to allow of easy readjustment of the separa- 
tors, v/hich may become disarranged in handling. 

10. To facilitate the lifting of the elements into the jars and to prevent the disarrange- 
ment of the separators when doing this, a short strip of webbing should be used. Lay thi.s on 
the board under the element. When putting into the jars, be careful that the direction of 
the lugs is relatively the same in each case, thus causing a positive lug of one cell to always 
connect with a negative of the adjoining one, and vice versa. This insures the proper 
polarity throughout the battery — bring a positive lug, at one free end and a negative at the 

11. Before lx)lting or clamping the lugs together they should be weU scraped at the point 
of contact to insure good cxjnductivity and low resistance of the circuit. Tliis should be 
done before the elements are taken apart and directly after unpacking if the battery is to be 
set up at once. The nuts should be gone over and tightened several times after the lugs are 
l^t fastened together to insure thoroughly good connection. 


12. Before putting the electrolyte into the cells the circuits connecting the battery with 
the charging source must be complete, care being taken to have the positive pole of the charg- 
ijig source connected with the positive end of the battery and so with the negative poles. 


13. The electrolyte is dilute sulphuric acid of a specific gravity of 1.210 of 25° Beauni6, as 
shown on the hydrometer at temperature of 70° F. If it is not convenient to procure this 
from The Electric Storage Battery Company already mixed and ready for use, it may be 
prepared by diluting suitahle commercial sulphuric acid or '* oil of vitriol," as it is more com- 
monly called, with pure water. Th^ acid as weU as the vxUer must be free from impurities, 
such as iron, arsenic, nitric or hydrochloric add. This is absolutely essential. When diluting, 


the acid must be poured into the water, not the water into the acid. The proportion of acid 
(of 1.840 specific gravity or 66^ Beauni^) and water are 1 part acid to 5 of water (by 
voluroe). The acid must be added to the water slowly and with great caution on account of 
the heat generated. The final density of the solution (1.210 specific gravity) must be read 
when the solution has cooled. The vessrl used for mixing must be a lead-lined tank or 
one of wood, which has not been used for other purpose^. A new wash tub or spirits barrel 
is recommended. 

14. The electrolyte should cover the top of the plates by one-half to three-fourths inch, 
and must be cool when poured into the cells. 


15. The charge should be started at the normal rate (the eight-hour rate of dischai^ 
as given fn the catalogue) as soon as the electroljrte is in the cells and continued at the 
same rate, provided the temperature of the electrolyte is well below 100° F., until there is 
no further rise or increase in either the voltage or specific gravity and gas is being freely 
given off from oR the plates. Also the color of the positive plates should be a dark brown 
or chocolate and the negatives a light slate or gray. The temperature of the electrolyte 
should be closely watched, and if it approaches 100^ F. the chai^ng rate must be reduced or 
the charge stopped entirely until the temperature stops rising. From forty-five to fifty-five 
hours at the normal rate will be required to complete the charge: but if the rate is less, the 
time win be proportionately increased. The specific gravity will fall rapidly after the 
electrolyte is added to the cells, and then will gradually rise as the charge progresses until 
it is again up to 1,210 or possibly higher. The voltage for each cell at the end of charge 
will be between 2.5 and 2.7 volts and for this reason a fixed or definite voltage should not 
be aimed for. It is of ike utmost importance that this charge be complete in every respect. 

16. At the end of the first charge it is well to discharge the battery about one-half and 
then immediately recharge it. Repeat this treatment two or three times and the battery 
will be in proper working condition. 

17. After the completion of a chai^ (initial or with the battery in regular service) and 
the current off, the voltage will fall inunediately to about 2.20 volts per cell, and then to 2 
volts when the discharge is started. If the discharge is not begun at once then the pressure 
will quite rapidly fall to about 2.05 volts per cell and there remain while the battery is. on 
open circuit. 


18. A battery mvM not be repeatedly overcharged j undercharged^ averdischargedf or aRowed to 
stand completely discharged. After the initial charge is completed the battery is ready to 
be put into regular service. A cell should be selected as a ''pilot cell," that is, one that is 
in good condition and representative of the general condition of the battery. The height 
of the electrol3rte in this cell must be kept constant by adding a small quantity of water 
each day. This cell is to be used particularly in following the charge and indicating when 
it should be stopped. 

19. When the battery is in regular service the discharge should not be carried below 1 .75 
volts per cell at full load. Standing completely discharged will cause permanent injury; 
therefore, the battery should be inunediately recharged after a heavy dischai^. 

20. The battery should preferably be charged at the normal rate. It is important that it 
should be sufficiently charged, but the charge should not be repeatedly continued beyond that 
point. Both from the standpoint of efficiency and life of the plates, the best practice is the 
method which embraces what may be called a regular charge, to be given when the battery 
is from one-half to two-thirds discharged, and an overcharge to be given weekly" if it is 
necefisaiy to charge daily, or once every two weeks if the regular charge is not given so often. 

21. The regular charge should be continued imtil the gravity of the pilot cell has risen to 
within three f>oints of the maximum as shown on the last previous overcharge. For exam- 
ple, if on the previous overcharge the maximum is 1 ,210 then on the following regular charges 


the current should be cut off when the gravity of the pilot cell reaches 1,207, correction being 
made for temperature change, as noted below. 

22. The overcharge should be prolonged until all the cells gas freely and until no rise in 
the gravity of the pilot cell is shown for five successive fifteen-minute readings. 

23. Just before the overcharge, the cells should be carefully examined to see that they are 
free from short circuits. If any short circuits are found they should be removed with a 
stick or a piece of hard rubber; do not use metal. 

24. As the temperature affects the gravity, this must be considered and correction made 
for any change of temperature. The temperature correction is one point (0.001 sp. gr.) for 
three degrees chailge in temperature. For instanc(% acid which is 1,210 at 70^ will be 1,213 
at 61° and 1,207 at 70^. 


25. In order that the battery may continue in the best condition it is essential th/it gravity 
and voltage readings be taken on all cells in the battery at least once a week, the gravity 
readings on the day before the overcharge and the voltage reading near the end : the vnAtagt 
readings must always he taken when the current is fowingf openrcircuit readings being oj nt 
value. Also at the end of each charge it sliould be noted that all of the cells are gassing 
moderately and at the end of the overcharge very freely. 


26. If any of the cells should read low at either time and do not gas freely with the others 
at the end of charge, examine them carefully for pieces of scale or foreign matter which may 
have lodged between the plates; if any are noted, remove them by pushing down into the 
bottom of the jar with a strip of hard rubber. Never use metal of any hind for fhis purpoes. 
If the hard rubber is not easily procured at the moment a piece of hard wood may be used, 
but it is not advisable as a usual practice. 

27. If, after the cause of the trouble has been removed, the readings do not come up at 
the end of the overcharge, then the cell must be cut out of circuit on the dischaiige, to be cut 
in again just before beginning the next charge, during which it should come up all right- 

28. Impurities in the electrolyte will also cause a cell to work irregularly. Should it be 
known that any impurity has gotten into a cell, steps should be taken to remove it at once. 
In removal is delayed and any considerable amount of metal becomes dissolved in the 
solution this .solution should be replaced with new immediately, thoroughly flushing the 
cell with water before putting in the new solution. The change should be made when the 
battery is discharged and just before chai^ng. If in doubt as to whether the electrolyte 
contains impurities, a half-pint sample taken at the end of discharge should be submitted 
for test. The Electric Storage Battery Company will analyze and report on, free of charge, 
samples received with transportation charges prepaid. 


29. The accumulation of sediment in the bottom of the jars must be watched and not 
allowed under any circumstances to get up to the plate-s, as, if this occurs, unnecessarily 
rapid deterioration will result. To remove the sediment, the simplest way, if the cells are 
small, is to lift the elements out after the battery has been fully charged, draw off the acid, 
and then dump the sediment, getting the element back and covered with acid as quickly as 
possible, so that there will be no chance of the plates drying out. Acid, not water, will be 
required to complete the filling of the' cells, the specific gravity being adjusted to standard 
(1,210 at the end of charge) at the same time. 


30. Do not allow the surface of the electrolyte to get down to the top of the plates. Keep 
it at its regular level (one-half to three-fourths inch above the top of the plates) by the 
addition of pure ivater, which .should bo added at the beginning of a ichai^, preferably the 
overcharge. It will not be necessan^ to add acid except at long intervals or when cleaning 
a^ noted above. 




31. If the battery is to be used at infrequent periods, it should lie given a "freshening" 
charge every two weeks. 


32. If it is thought best to put it out of service for a time, then it must be treated as fol- 
lows: After thoroughly charging siphon off the acid (which may be used again) into conven- 
ient receptacles, preferably carboys, which have been previously cleaned and have never 
been used for other kinds of acid, and as each cell becomes empty immediately fill it with 
fresh pure water. When water is in all the cells, allow them to stand twelve or fifteen hours, 
then draw off the water. The battery may then stand without further attention until it is to 
be again put into service. Then proceed as in the case of the initial charge, as described 
above. If there is any considerable amount of sediment in the cells advantage should be 
taken of the out-of-service period to clean them thoroughly. 

Appendix L. 

To obtain this interval by deduction, let Q be the chai^ge on a Leyden jar whose capacity is 
CfP the potential to which the jar is charged, L the self-induction, and R the ohmic resistance 
of the discharging circuit, p the counter electro-motive force due to the induction L. Then 

J, the intensity of current produced bv discharge in time <=- - ^ but /?=--; therefore 

R at 

^^ dO o d^O 

J= P— ddt . Further, J=-^ and P=-^ ; .*. by substitution and transposing, ^-f- 

rj—Yrr A solution of this equation gives C=^, f ^, ^^A^e"^} . . . etc., where 

1 R I jyi 1 ~ 

jr, jTj are the roots of the equation, Lx^-{-Rx-{-q—Oj hence t= 2L~yAT'^~~ rri- 

If the roots are real, /? > 2 y , and the discharge is a diminishing one, but if the roots 

are imaginary, i. e., if fi < 2 y ,, then C=e ™"p" [^i (^oa Bt-^B^ Sin Bt,] where 
B=J y— _ — and the discharge becomes oscillatory with the period T= „. If ^y ^ is small 

conopared with-77,, which in the closed sending circuit abed (fig. 4) is the case, it may be 

2»r -^^- 
neg^ected, and hence r= -j»= I j —^^ >/!€, If V is the velocitv of the wave and \ 

the wave length, then X—VT^2nVhyiJ0. Now, the induction L and capacity C of the 
aerial wire varies as the length, hence the wave length A suited to any aerial wire is propor- 
tional to the length I of the wire, and by experiment it has been shown that A = 4/. 

Appendix M. 


Department of Commerce and Labor, 

Bureau of Standards, 

TTcwAin^on, , — — . 

1. An approximate formula for the calculation of self-inductance is given by Maxwell, sec- 
tion 706, Volume II, Electricity and Magnetism, as follows: 

L„=4;r»»o(«o?.5-2) (1). 

where a=mean radius of the coil, n = number of turns of wire, and R is the geometric mean 



distance of the cross section of the coil. All dimensions are in centimeters, and the loga- 
rithm is Naperian. Lis then in centimeters, and to convert it to microhenrys, divide by 

2. The above formula assumes that the current is distributed uniformly over the cross sec- 
tion of the coil, as it would be if the wire were square and insulated by a covering of infinitesi- 
mal thickness. For the case of round wire insulated by a thicker covering the self-induct- 
ance is greater than that given by the formula, as Maxwell points out, section 693. This cor- 
rection consists of three parts and is represented by the following expression: 

J L=4ir na flog^ ^+0.13806+^ J " (2). 

where JL is the correction in L (in centimeters), a and n are the radius and number of turns. 
as before, D and d are the diameters of the covered and bare wire, respectively, and ^ is a 
constant depending on the number of turns of wire in the coil. (The correction 0.13806 is 
the increase in self-inductance of the separate turns because the wire is round- instead of 

square, log^ -^-is the increase because the wire is smaller than the square wire assumed in the 

formula, A is the correction due to the difference in the mutual inductances of the separate 
turns on one another, being more for the round wire than the square.) For a coil of few- 
turns^ is about 0.0150. For a coil of many turns it is as much as 0.0180. This part of the 
correction is small and is not of much importance in coils used for wireless telegraphy .<i 

3. The calculation of R, the geometric mean distance of the section of the coil, is a tedious 
process for rectangular sections. The formula is given in MaxweU, section 692. If the sec- 
tion is a square^ 72=0.447 &, where h is the length of one side of the square section. 

4. Stefan's formulaic for self-inductance is more exact than Maxwell's approximate for- 
mula. It is as follows: 



o o oo 


Axis of coll. 

Here a and n are the mean radius and number of turns (as in Maxwell's formula), b is the 
over-all breadth of the coil, c is the depth, and y^ and y^ are constants depending on the ratio 
of the quantities b and c (always dividing the smaller by the larger), this ratio being called 
X. A copy of these two tables is appended to this report. 

This formula is quite exact for the ideal case of square wire insulated by a covering of 
infinitismal thickness, but requires correction just as formula (1) does for the usual case of 
insulated round wire. 

5. Example 1. Coil of 18 turns, a=10 cm. Suppose Z>=J cm. 

6= 2 cm. d=l cm. 

6=2 cm. c= 1 cm. D_ 






c=l cm. c 1 

From Table 1, y, =0.79600 
From Table 2, ^2=0.3066 

aThe Bureau will shortly publish a table of values of A for coils of various numbers of turns. 
No such table has ever been published. 
Wied. Annalen, vol. 22, p. 113, 1884. 


By formula (3) 


f^«v/4'n0+'^0--'^"-i(io(-^^ ■ 





• fo?o v/5= 




13 80 
9,600 ^^^ v/ 5 ~ 






.-. 4=4;rx324x 10X2.78692=113470 cm. 

=113.47 microhenrys. 
Then ^L.=4»'na{^^2 -.13806 i .0150} 

=4n'Xl80X.8462=19l4 cm. =1.914 microhenrys. 
.". L=Lo4-^X,=ll5.38 microhenrys. 
P^xaniplo 2. Coil of 24 turns, a = 10 cm. 

6= 1.91 

cm.| 6^ = 

= 3.6481 

c= 1.28' 
= ^= 0.67 

cm. f2- 
&2 + c2 = 

= 1.6384 


= 5.2865 

From Table 1 
From Table 2 

, Vi =0.82932 
l,y,= 0.4460 


80 _ 


9,600 ^^""^^ 

80 _ 



< 0.4460 = 





..L^ = 4itX (24) 2X 10 X 2.72580. 

For the correction Z>=.318, <?= .109, ^=2.9174. 




.0150 • 

.•.^L=47rnaX 1.2238 

=4 Tcn^ a /"1:2238\ ^^^^^ ^^24 

. L=L,^JL=407CXC24y (2.7258 r-0510) 
=201.000 cm. =201.0 inirrohenrys. 



By varying the size of coil and number of turns any particular value of the self -inductance 
can be obtained . For accurate work the dimensions must , of course , be taken very carefu Uy . 

6. When the taction of the coil is square the formula is simpler. Then 6 = c and . 

I„ = W«{fo,,^(l+2j,)+.0365^^ -1.19491} ^.^ 

L =L^-^JL9s before. 

7. For a single circular turn of round wire, the mean radius being a as before and p being 
the radius of the circular section of the wire, 

L = 4.a{/<^.^(l+^,)-1.75-.00835} (5) 

This is a very exact formula, and requires no correction. Very approximately this is 
L = 4it(j/log^ ^—1.75^ (6) 

S. W. Stratton, Director. 

Table L 





















1 0.60 



' 0.65 









1 0.80 



1 0.85 



j 0.90 








Table IL 

•' - - - - 









0. 1418 


0. 1548 


0. 1714 


0. 1916 

































\ ■ 

. \ 

.\ 1 '* •. 



.-? : < \ 


,, i'. -< A i^ ^ 

n • THi! 


•■F.r'i>lTTi ; 

,»^ .*•■ 








I ■-.- ■ » ..'' 


■^ ^ /.' ff ;\\ 

.K >.-^ 

^ • 


^A' 'S^- 

'•f' .s ■• , *•■ 





^^ s S.'Jj; .y. .. 




or THE 





or rHF 




fi or -THf * \ 







/ or THf 


.1 He'? 



Plate XIII. 

A£^AL mM£ 
























or rHF " 







S»6I I n^y, 
SEP 3 1915 

DEC 161915 
MAY 28 1917 


nm 20 1918 

JUL 13 1918 
AIM d19l8 

30m- V 15 

re 1 0bb87 

r r